[MC-129682] Hostile mobs don't spawn after upgrading from 18w16a

Playing in hard mode, locked, hostile mobs don't spawn. Tried /gamerule doMobSpawn true and changing the difficulty using the /difficulty tag. But nothing has worked thus far. Mob spawners still spawn mobs from what I've seen so far.

Update: Hostile mobs are spawning, just very seldom. Also, it seems like the mob cap is very low as I've only seen a max of five mobs spawn in at once. (four pigmen and one ghast.) I haven't been to the overworld yet since this discovery. I will update when I have more info.

Update 2: Overworld hostile mobs spawn, too. But also seldomly.

Linked issues

is duplicated by 4

MC-129816 Mobs not spawning in 18w20c Resolved

MC-131493 Endermen do not spawn in the end. Resolved

MC-131666 Light everywhere at morning Resolved

MC-135804 1.13 endermenspawns very strange in the end Resolved

relates to 1

MC-130964 Aquatic mobs spawn extremely rarely when upgrading from 18w16a Resolved

Attachments

Comments 15

Ahmad Al-Yousef 2018-05-16T08:15:31Z

I moved my world from 18w16a to 18w20a and the same thing happened to me. Hostile mobs don't spawn. So I went to chunks that have not been generated before and hostile mobs spawn there fine.

It appears that hostile mobs don't spawn in old world generation. But they do in new world generation.

montuos 2018-05-16T14:45:32Z

I came to report that my spider and skeleton spawners were no longer working in 18w20a, but this bug report could easily be the explanation for that.

I too updated my world from 18w16a. I've been switching back and forth between survival at normal difficulty and creative mode. Either way, the spawners don't spawn anything. My base and caves are well lit, verified with spectator mode, so there aren't any hidden underground mobs maxing the mob cap.

Jeff Carter 2018-05-16T14:55:01Z

I also have a world from 18w16a that I updated to 18w20a and ran into this problem. I figured something was up when I AFK'd for ~8 hours next to with & iron farms with 0 drops.

Gan Quan 2018-05-17T01:57:33Z

Confirmed in 18w20b.

How to reproduce:

Create a world in 18w16a with cheats on.
Teleport to somewhere away from the original region. (not sure if this is necessary)
Explore around the region a little bit(not sure if necessary)
Convert the world into 18w20b.
/set time night
No hostile mobs will spawn.

Joby Walker 2018-05-17T03:39:07Z

I'm seeing the same thing in an upgraded 18w16a world where spawning is extremely rare and spawners don't seem to work. The only exception is a partially built Slime Farm that is producing huge amounts of slime balls.

5 more comments

Joby Walker 2018-05-17T15:46:09Z

This seems to happen because all areas are getting skylight access and that never changing. This means underground slimes will spawn like crazy, while other mobs just don't happen. Attached image showing an underground area with skylight level of 14.

Gan Quan 2018-05-26T01:09:42Z

Confirmed in 18w21b.

Mobs do spawn in underground; they never spawn under the sky (the same for the End) in chunks created in 18w16a.

Linda A. Wingfield 2018-05-26T08:48:46Z

I came in to report that none of my grinder spawners are working in 18w21b. They didn't work in 21a, either.

The world in question is a single player world, started in 1.12.2, then migrated through the snapshots. Though I couldn't even take it into 18w19a, 19b allowed it to correctly form, and the spawners worked correctly.

Taking it into 18w20c was fine. I had no problems with the spawners.

In 18w21a, the spawners didn't work, but when I gave up and put in a fresh (backup) copy of the world, the spawners did work...until I went and did a few other things, then went back to the grinders, and then they no longer worked.

As soon as 18w21b arrived, I put in a fresh copy of the world and tried again. Very early yesterday morning, the grinders worked. Now, early this morning, after doing some other things and going back to try again...nope...not working. The figure of the mob is going around inside the spawner, but there are no sounds, and nothing ever is actually spawned.

Other hostile mobs in the area seem to be spawning just fine...it's just the spawners/grinders that are having problems.

UPDATE: I tried again, with a copy from 18w20c, which was working fine. Opened in 18w21b and went to one of the grinders...mobs spawned normally. Quit the game and went back in. As long as I remained there and went nowhere else, the spawner worked correctly.

Having noticed that someone reported that the lighting wasn't working correctly at some point, I took note that the lighting in the "killing room" was correct.

After several tries of quitting and going back in without going anywhere else, I then traveled to another location, and then back to the grinder again. No more spawns after that, at all. I then took note that the light inside the "killing room" was totally bright, as was everything else underground in that area, even where there were no torches!

So...obviously, after I left the area, then went back, something happened with the lighting, which would explain why the spawner was spinning, but nothing would spawn...it wasn't dark inside the spawning area, as it should be.

I'm not going to play this world until the next snapshot, then I will try again.

Linda A. Wingfield 2018-05-26T10:29:53Z

Instead of editing, I decided it would be better to add another whole comment. I've gone back into the game, now, in 18w20c, and have now found that the same anomaly actually happened starting with the copy from when I first ported the world into 18w20c from 18w19b (which was directly from 18w16a).

I had only gone to my grinders one time in 18w20c, and just assumed that they worked correctly. Such is not the case. If I put that fresh backup copy in, I can go in and the grinders (one skeleton, and one spider) work great the first time, with the proper lighting, but as soon as I go somewhere and go BACK to each one, the lighting is messed up (totally bright and no way to make darkness happen again), and the spawners no longer work.

Gan Quan 2018-05-30T04:17:53Z

Still occurs to me in 18w22a.

- 2018-06-03T23:51:41Z

This bug can be solved by modifying the NBT tree of the world:

Back up your 18w16 world.
For each chunk of each region, including the Nether and the End:
1. Locate the Level node.
2. Locate its Heightmaps subnode.
3. If its empty, leave it as is.
4. Otherwise, save the list of values in its LIGHT subnode, or in its SOLID subnode if the former is not present.
5. Remove everything in the Heightmaps node and replace it with 4 subnodes (of type LongArray) with the following names: LIGHT_BLOCKING, MOTION_BLOCKING, MOTION_BLOCKING_NO_LEAVES and OCEAN_FLOOR. In these nodes, put the list of values you've got in the previous step.
Open Minecraft and convert your world to the last snapshot.

If you've got a program able to do this kind of modifications, don't forget to convert your sea grass, too.
Hope this helps!

Matt 2018-06-05T15:52:24Z

Still occurs in 1.13-pre1 hard mode. Overworld hostile mobs spawn seldomly. Dark caves have literally max 1 hostile mob.

Edit: Problem seems to occur mostly in caves, very few or no mobs there.

Matt 2018-06-07T07:11:39Z

I thought only caves are affected but then I've compared 1.12.2 and 1.13-pre1 and there is a huge difference in mob quantities above ground too.

Yann LAPEYRE 2018-07-18T18:13:19Z

It seems to be fixed for me on 1.13 with the "optimize world" button, my xp/gold farm on the roof of the nether restart spawning, same as the chunks i ve already charged long time ago. Hoping it ll works for you all too.

Jacob Potter 2019-02-17T01:44:24Z

I'm having this issue in snapshop 19w07a in my world that I first made in early minecraft 1.13 snapshots. Those flying creatures that spawn when you dont sleep still work but no other hostle mobs in the overworld will spawn ever. I hope there is a way to fix this.