I've experienced an issue where slimes are no longer spawning in a slime chunk. I've only noticed this in 20w21a ( I've not looked at other snapshots ), the same chunk however in 1.15.2 is spawning slimes.

I've tested this using the same seed and the same chunk coords in both versions using the same method of clearing out the chunk to Y 5 lighting sufficiently exactly the same and sitting idle on a platform above in 1.15.2 slimes spawn however in 20w21a no slimes spawn I left both version running for about an hour each. I did not light any additional areas around the chunk in either version. Both worlds had been created in their respective version freshly, this was done in a badlands biome. 

I've searched for the last few days to find if its related to something else but I'm not finding anything referencing slime spawn changes. This may well be working as intended but I'm not sure