Mob farms and structure farms not spawning mobs or spawning too few mobs

Having the same issue.

My once super active mob farm has had no spawns after an 8 hour afk session.

I did some testing on this bug. What it looks like happened is when Mojang fixed the issue with mobs spawning on blocks they weren't supposed to, they actually instead of only removing the ability for mobs to spawn on those blocks (glass, bottom half slabs, blocks with buttons, signs, etc on them) they actually made it so the mobs wont spawn anywhere at all on that Z axis.

Confirmed in 1.14.1 on Windows 10.

Prowl is correct, but it affects a lot more blocks than just leaves, glass, stairs, and bottom slabs. It looks like most non-solid blocks have the problem, including things like walls, fences, chests, grass path, lanterns, anvil, stonecutters, and many more. My list is up to 34 items so far. If one of these has sky access, nothing will spawn below it at any Y level.

It's easier to list the non-solid blocks that still allow spawns below them:
Carpet
Top slab
Top Snow (1-7 layers)
Redstone Dust
Redstone Comparator
Redstone Repeater
Redstone Torch
Rail (any type)
Scaffolding
Torch
Sea Pickle
Grass
Double Tallgrass
Fern

Impact: This bug eliminates or seriously reduces the spawn rate of:

• Anything in biomes with dense foliage, including roofed forests, jungles, most kinds of taiga, and to a lesser degree birch and regular forests. Wolves, foxes, pandas, ocelots, and parrots will be almost nonexistent.

• Witches in witch huts.

• Guardians in ocean monuments

• Monsters in woodland mansions

• Monsters in caves under crop farms, most buildings, and any area where the surface has been paved with slabs and stairs or covered with leaves as a spawn-proofing measure.

In a newly created world, there may not be enough animals spawning near the player to keep them fed, forcing them to explore for food before they even have basic shelter. They may not be able to make a bed for several days, forcing them to waste health fighting monsters or to be bored waiting in a hole for the night to pass. It could totally spoil the early game experience and make the game seem much more difficult than it should be.

Yeah I figured that was the case. Good thing I got a good afk session in before the update. On the blocks with buttons, is that only on the top of the block and not the side, prowl? That’s the basis of my mob farm and haven’t had an issue before this.

The Bug. When the highest block at a position is glass, leaves, or a similar spawn-proof block, the Spawner::tick algorithm cancels all surface, cave, and mob spawns on that tick.

The Cause. This bug is caused by the hotfix for MCPE-54241, which was implemented in the wrong location. As a result if the search for a surface spawn position terminates early because it encountered glass, leaves, or a similar block, the game now detects this situation, but will skip the rest of the spawning algorithm.

The Fix.  Move the test of the return value of the first call to findNextSpawnBlockUnder after structure spawns are processed and right before the call that will spawn surface mobs. findNextSpawnBlockUnder also has to be updated so it doesn't set the the y-coordinate of the search to -1 whenever it encounters a non-spawnable block when search for a surface spawn spot. Make sure that if the test fails, that only the surface spawn is canceled. Cave spawns should occur even if the search for a suitable surface spot was unsuccessful.

An Example. I've uploaded a test world with 4 pillager outpost spawning areas on grass. When they have sky access, surface, cave, and structure spawns occur. When they are under glass or leaves, all spawns are canceled. Only the highest block matters. When stone and glass above the grass and outpost spawns, you get the expected behavior of cave and structure spawns.

Quick fix for mob farms. If you have mob-proofed the top of your far with bottom slabs, use carpet instead.

Oh no!!! Everyone has mob farms and loves them! Hopefully this will get fixed soon

Can confirm the carpet fix works.

Thanks for getting this reported so promptly, and for all of the useful information provided by all.

just want to make sure ? mobs cant spawn on carpet ?

is this an intended issue tbh it could help alot getting rid of unwanted cave spawns I kinda could see alot of potential if so

@unknown: Mobs cannot spawn on carpets. That is by design and is working as intended.

Mobs not spawning under certain kinds of blocks is absolutely a bug. The intended behavior is that the type of block on the surface should determine which density cap a spawned mob is counted against, not whether it spawns at all. The bug also reduces not just monster spawns, but animals as well.

Tried the carpet fix at top level of my spawning platforms and still seeing this issue.  Playing on Nintendo Switch, farm is built at y=216, so mob cap should not be taken up by anything on surface level...what am I doing wrong here...?

@unknown: Did the farm work properly prior to 1.14.1? What is the Y coordinate of your carpets, and what kind of block is immediately beneath them? How many spawning platforms are there, and what are they made of? A screenshot from the side might be helpful.

The first thought that came to mind is that your carpets might be at Y=255 and the game logic might not be looking that high for the sky access block. But I tested that and monsters spawned under the carpets, at Y=73 in my case.

It looks like im getting a handful of spawns now, but nowhere near what i was getting previously... Maybe 2 per hour of afk in the sky. Does this possibly have something to do with mob cap due to lack of despawning? I will attach pictures as soon as i can

In the overworld, the search starts at y=256, so carpets at y=255 are okay.  William Allard, try peaceful cycling your farm to see if that improves rates.

Good diagnosis, Reed

We're using a version of SilentWisperer's original Raid Farm, which has had zero captains spawning since the updates. If you go there with bad omen already attained, the raid farm works as intended, but no pillager patrols will spawn nor captains to start the raid.

Can anyone advise what we would need to do? I've tried placing two stone blocks and carpets on top of them at the highest point above the same coords where the spawns would generate down further in the outpost. But that seemed to have no effect at all.

Is this workaround only good for traditional mob farms such as creepers, etc?

@William Allard the mob density caps have nothing to do with Y-level, so they can be taken up by mobs 200 blocks below you. The fact that you got a couple mobs suggests that you do have mobs down below taking up your caps. Did peaceful mode cycling work? What is affected by Y-level is where where new spawns can take place: spawns can only occur in a spherical radius around you from 24 to 54 (ish?) blocks away. So for a platform at 216 to spawn you have to be under it at about 170-190, and nothing will spawn down on the naturally generated surface while you are at that level. However, if stuff spawned on the surface or in caves before you got up to that level, it will count against the density caps for your farm, and slow down or stop its production.

@Jay Sirrom this workaround is for both regular spawns and structure spawns, and based on what you've said your outpost should spawn. The outpost spawns also have their own cap separate from regular surface and cave density caps. Are you sure that no pillagers glitched out and got lost in caves and are taking up the cap? You mention placing only 2 stone blocks–maybe make a wider platform of blocks in case you got the spawn coordinate off by a little? Spawns occur on the northwest corner of blocks so its easy to mistake the actual coordinate they are using.

This work around doesn't work for my raid farm. I have maybe 1 or 2 pillagers spawn every 10 minutes at a platform that I even expanded for testing. I used commands to kill any pillagers in the area, but there were none to kill. I killed all mobs, and still nothing. Setting game to hard mode makes no difference.

This raid farm worked as intended in 1.13 and 1.14, but broke in 1.14.1. Carpets make no difference. I filled up the whole Y coordinate with blocks and just left the rest open above the spawn platform.

I can take a picture of an empty spawn platform, but that seems kind of meaningless.

Same with witch huts: a lot of hut, no witches.

IM HAVING THE SAME ISSUE, I have my farm at Y200 and in 1.12 I was getting drowns, witches, zombies, creapers, skeletons, Cod, squid, dolphins, and spiders and NOW NOTHING SPAWNS!! I have spent so much time and resources on this farm and now, even in my base below NOTHING SPAWNS EVEN WITH NO LIGHT. I can't even get a fish, PLEASE FIX THIS ISSUE, you have already broke my kelp farm please this is a game breaker for me!!

In case you didn't notice, there is a workaround in the description above that should solve the problem for most people until a fix has been issued.

Please remember that the bug tracker is not a discussion forum. Its purpose is to collect information about a bug and forward it to the developers. Comments should be used to provide additional information about the bug to the developers. For this bug, such information might include how your farm is constructed (especially the roof) and what kind of mobs, if any, still spawn in it.

Workarounds, when available, are provided as a courtesy. Although they have helped some people, we cannot guarantee they will work for your situation, and if they don't it just means you need a different workaround, or there is no workaround for your situation. The failure of a workaround to provide relief is not itself a part of this bug and is not something the developers will be working to fix, since once the bug is fixed the workaround will no longer be needed.

Mega_Spud (Jay Wells) thanks for commenting on this bug so we know it has reached the ears of those who can solve it.

@Jay Sirrom fixed silents raid farm by going up to y=200 and building a solid block platform over the whole spawn platform

Confirmed that Christopher's additional clarification for the fix worked great. I am posting some screen captures for those are attempting this workaround for a standard raid farm.

• Cobble platform placed at Y level 200. It covers the entire spawn area below it with a one block overlap in each direction. carpet is then placed on every block at the Y 200 level. Captains spawn correctly and raid spawns do not spawn on top of the platform as they did when the platform was just a few blocks above where the spawn platform exists for the farm.

See captures 

Raid_Farm_Level_y_200_Screenshot_001 through Raid_Farm_Level_y_200_Screenshot_003

My guardian farm stopped spawning any guardians. The mob cap can't be an issue, because I used a repeating command block killing everything but guardians.

There are solid blocks under the water source, so guardians should be able to spawn.

The roof consists mainly of solid blocks and top half slabs, so the bug which blocks all spawning attempts shouldn't be an issue either.

I've tried the workaround described in the comments (roof at y=200 with solid blocks and carpets) and I've tried direct sky access. Both methods yielded no results.

All: Please keep in mind that the bug tracker is not a discussion forum. Comments are meant for providing additional information about the bug to the developers. We also welcome comments that share workarounds, but in general, interacting with other users is best done on sites like Reddit or the Minecraft Discord. Thank you for your cooperation.

This bug is fixed in the latest beta version, and the fix will be included in a future update when that is ready for full release (no specific date can be given). We will leave this ticket open as a point of reference until the fix has been fully released.

Fix is now included in the regular release.

Still not exactly what was reversed, but at least glad to report that the Raid Farm that used the workaround posted is still functional on our realm after the 1.14.20 update. I had been fearful this reversal was going to break that.

This was rolled back right?

Not supposedly.

Yes, it was; spawning is back to 1.13 behavior or something close to that. As a consequence, MCPE-41273 was reopened.

I must be confused then. I thought the question was about MCPE-59682 being rolled back to when it was broken in 1.14.1. As far as I know that has not happened and structure spawns still work. Is that NOT correct? Is this broken again? 

The 1.14.1 behavior described in this bug report, as well as the 1.14.0 behavior described in MCPE-54241 and MCPE-58670, were rolled back in 1.14.20. As a result, 1.14.20 and 1.14.30 should have the same spawning algorithm as 1.13. (Please note though that I can speak only on the basis of my own testing and the comments of other users, especially the comments made on MCPE-41273 since 1.14.20 was released.) If you think there is something else amiss please do provide whatever information/evidence you have.

Ok. I thought the question was regarding changes in the new 1.14.30 update. The "rollback" was in 1.14.20.

1.14.30 on Android mobile. My witch farm and raid farm are broken. Witches don't spawn in hut, pillagers/captains do not spawn at all. Tried the carpet trick but no change

@Gary the specific bug that this report describes was fixed. There is probably some other reason your structure-based farms are not working. I suggest you get some help with you farms from the community on the Minecraft forums, Reddit, or Discord.

I am experiencing the same problem - my outpost spawns loads of pillagers but never a captain on PE 1.14.3

@Lauren this bug report is about mob farms and structure farms not spawning anything at all. That was due to a bug in which certain roof-top blocks were preventing all spawns below. If you have some pillagers spawning, then this is not your issue.

It is possible that are not getting captain spawns because there is already a captain somewhere within 4 chunks (64 blocks) of the outpost.

We will be tracking the issue of Pillager spawns at outposts but no captain spawns since 1.14 at at MCPE-60560.

Can confirm this bug is back in 1.19... I've built 2 different versions of a raid farm and both failed...

EDIT: The previous work-arounds appear to make no difference to the spawns.