Slimes spawn less frequently if there are any blocks above their spawning spaces

Cannot reproduce, slimes do spawn underground just fine for me

Since the 1.14.3 version was marked as duplicate add it to the affected versions

Slimes don't spawn in spawn chunks on my 1.14.4 server but they do spawn in swamps

Cannot reproduce. Please provide world seed and slime chunks coordinates if you have this issue.

Slimes dosen't spawn on my singleplayer word in slime chunks. Tried in multiple chunks, multiple times, for a week now. Still not a single slime spawned. The world was generated in the early snapshots of Minecraft Java edition 1.14

https://bit.ly/2GJrp5I Here is a world download of my survival world, where i came accross and tested the issue. The world was generated in the early snapshots of Minecraft Java edition 1.14. Now playing  in 1.14.4

Slime spawn rates in slime chunks are negligible compared to same conditions in 1.12 and 1.13. Unless the whole chunk is mined out the rate appears to be negligible.

Chunk 0 0 -5, has had one spawn of the test world I attached, this is negligible to the rate prior to 1.14. Chunk 3 0 -2, have been experiment with. Currently with glass, but the rate is severely cut from having no block above the platform.

I have checked the attached world and it seems like slimes are indeed spawning, albeit at a much slower rate than previously.

What could be the reason for the "much slower rate"? 

As of 1.14, all blocks other than air raise the max height of any particular (x, z) coordinate. Every slime spawn attempt at a particular (x, z) coordinate is distributed from bedrock to the corresponding max height. In previous versions, blocks like water and glass didn't raise the max height, so you could simply bomb a little hole in the bottom of the ocean and cover the top with glass to make a slime farm. Now in 1.14, you need to remove every block above the farm to get the same rates as previously.

It also helps significantly to dig out an area about 20 blocks out from your slime farm (as well as all blocks above this larger area), as this drastically increases the chance that spawn attempts will start in adjacent chunks and make their way to your slime chunk due to how pack spawning works.

In my testing I applied a glass roof and the rate appeared to have at least halved. Efficiency of a farm isn't the problem. I usually create a farm close to my base, passively generating slime and letting their own pathing algorithm remove them from the platforms. Now, to get any rates similar to 1.12 and 1.13, I have to create a hole, which I don't want near my base. Since its not near my base, i have to afk at it. As a casual player who wants to build a design using slime, but i am required to build a farm that would take 6 hrs compared to an hour, I am not inspired to play.

Efficiency isn't the problem when the spawning algorithm has changed, making spawn rates negligible unless you are trying to make a efficient design.

Alright, I have edited this ticket so that it actually includes that blocks above the spawning platform decrease the spawning frequency immensely, and I was able to confirm that.

While killing all other mobs that were spawning, in the slime chunk with no roof, 18707 slimes spawned, while in the one with a bunch of blocks above it, only 1369 spawned.

I repeated the experiment with glass instead of sandstone above the chunk with a roof, and here the numbers were similar (18082 without roof, and 1307 with glass above).

This is WAI. Since light went to its own thread, spawn algorithm uses a different heightmap to determine topmost spawnable block as the top block that is not air, rather than top block that is not transparent. There is no other heightmap that the spawning algorithm could currently use. That change was deliberate and intended. Just remove all the blocks above your farms and not worry about it.

Yes. The question is only, is it intentional that slimes have become way more rare than previously or is it an unintentional side effect of those changes? Of course the new behaviour can be explained with the new lighting engine from 1.14, but that doesn't mean that slimes underground were supposed to become rarer.

Oh interesting, I thought something was goofy-