Slimes despawn instantly

Likely unrelated to the bug, but your crash report does not match the environment field you filled in above:

Operating System: Windows 7 (amd64) version 6.1
	Java Version: 1.7.0_45, Oracle Corporation
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation

Can you please clear this up? I would highly recommend removing anything but the latest version of Java from your computer for security reasons unless there is some (odd) reason you need to keep them.

Oh my... OK it seems Java auto-update doesn't update the 64 bit version, as my 32 bit version is 7u55, not 45. Sorry for that. Fixed!

Would you also want me to generate a crash report during night time, as you'll see all the hostile mobs too?

Yeah, no clue why Oracle refused to make the 64 bit auto-update on WIndows... Such a lovely "feature"

Yes, please attach an updated crash report showing that situation.

OK I attached a nighttime crash report. Bunch of mobs, no slimes.

Confirmed. Created test world customized with a biome set to only Swampland. Created a bunch of command blocks on a rapid timer to kill all mobs except slimes. Set time to night, difficulty to hard, and you will see a very few slimes get created and stay, but a bunch flash in and out just like the slimes-on-peacful issue.

Still exists in 14w21b.

Yes I noticed too. I hope it gets fixed. All those awesome new features with pistons and slime blocks are worthless if spawn rates remain at 3-4% of what they were before.

To add to what Fienxjox said, I also set a customized world to swampland only, created a bunch of command blocks to kill all mobs except slimes, and then ensured it was a full moon. Still most slimes flash in and out, with very few slimes actually remaining spawned. Needs fixing.

This was in 14w21b.

Yep, having the exact same issue.

I know in 20a there was a bug where no hostile mobs would spawn, which was immediately fixed in 20b. Perhaps whatever was keeping them to spawn is now keeping slimes from spawning..?

In 14w20a, something was changed in the slime's spawning system.

From wiki on 14w20a:

"Slime sizing was moved to a post-spawn method, so the slime's canSpawn() method would report spawnability based on the initial size, not the final size. There is an added secondary check which fixes the issue."

My bet is, this secondary check is exactly what is causing the issue. The canSpawn() method allows the spawning, the secondary check denies it over 90% of the times. You see them spawn, then vanish, all within a tick or two.

Definitely needs fixing!

I see this too, Kinda makes the game unplayable at the point where you need slimes, I think this has been an issue for me for at least three patches including the latest 14w21b.
I would also like to say that finding this using the built in search is not easy, in part cause all of the old postings about slimes, and that it wont let me change the display order.

I am having the same problem, and I am at a point in the game where it is very difficult to move forward without slime.

I have a classic slime farm on our server (still running 14w20b), and before that issue it could fill a double-chest of slimeballs in under 8 hours. Now it's been 9 days, probably more than 60 hours of gameplay, I have a bit more than a single chest of slimeballs. I can't supply anymore!

Can confirm that this is happening both in slime chunks and in swamps. Haven't seen a single slime in either... help?

I too have seen slimes appearing and then instantly disappearing in my superflat world, and in a swamp in a normal world. I didn't see a reduction in magma cube spawning in a very quick test, nor does it seem likely since they don't have the chance to randomly fail to spawn that slimes do.

It appears that the earlier comment is correct: when randomly-spawning mobs, it checks if the mob can spawn at the location. And then for slimes it checks again after spawning. The problem appears to be that slime spawning has a probability of just randomly failing, and this is applied each time the "can spawn" method is called.

So for slime chunks, each "can spawn" check has only a 10% chance of succeeding. Making it pass the chance twice reduces the successful spawn rate to only 1%. Swamps are more complicated, as there are three random number checks (a 50% chance of failing, a chance based on moon phase, and a chance based on light level) that all get repeated. Superflat reduces the chances further by failing on 75% of calls, meaning a superflat that's hitting the slime chunk spawning chance has its probability reduced from a normal 2.5% to only a 0.0625% chance.

Speaking of the slimes' reduced chances of spawning success, I wonder if these need to be rebalanced or even eliminated since slimes now despawn like other mobs when over 32 blocks away, instead of staying around until all players are 128 blocks away.

Same issue, doesnt seem to affect magma cubes btw as they are, in my world, spawning at highrates. Also, not relevant but I agree the spawning algorithm for slime need to be redone. IMO they should spawn along with other mobs in all chunks but still below y40 and swamps should remain as is witb surface spawns.

I'm seeing this as well.

Several minutes of testing in creative confirms this for me on 14w21b. Win7 64bit, Java7 u55

Tried traditional superflat. Slimes immediately being to spawn but instantly despawn. 5 minutes of hovering around yielded only 1 med slime that did not despawn, though he was gone immediately upon reaching 40 blocks of distance.

Loaded a new seed, located a swamp biome and set time to night. Again, slimes try to spawn immediately but instantly despawn. 5 minutes of hovering around again yielded only 1 med slime that did not despawn. 1 large slime spawned and remained as well, but was 40+ blocks away and despawned after 1 hop.

I play on a snapshot SMP server, and currently slimeballs are the most precious resource. I have yet to see or hear one in a week of play.

Still not fixed in newest pre-released. 12w25a

Slimes still despawning in swamp biomes.

Before 14w21b, slimes were spawning well... everything after, slimes appear and disappear. My high yield slime farm is now basically broken. 5 or 6 slime balls every 15 mins or so. Witnessed in the new 14w25a as well.

Edit: Tested in 14w25b and it appears to be a lot better if not fixed completely! The new AI decreasing Farm yield, but lets face it, it was way to OP before... Seems about right now. Thanx for the community support Mods!

Awww, man! I expected this issue to be fixed in the newest snapshot. There are several redstone projects on hold because I can't get enough slimeballs. I really hope this issue gets the priority it deserves. BTW, I've been playing 14w20b.