Mark Loit

I don't believe this to be a bug. I used the OP's seed and the datapack with 1.17.1, and had slimes spawn at the OP's y7 level. For testing I created a 17x17 chunk perimeter centered on the OP's coordinates for his slime chunk. [Also confirmed via chunkbase that it is indeed a slime chunk] As you can see from the attached photos slimes are spawning. So rather than a bug I believe this is just a matter of the OP not spawn proofing the surrounding area sufficiently. As mentioned earlier, with the datapack there are a lot more caverns and caves underground, creating fertile ground for mob spawning, so the mob-cap could easily become filled up before the slimes get a chance to spawn.

I had similar thoughts when I wasn't getting any slimes after digging out a 4x4 chunk area at Y12 on a server I play on. So I did some testing in a creative world with the datapack, and can confirm that slimes do still spawn. My guess is that due to the high number underground voids created by the datapack, the spawn rates are much lower as the mob-cap is consumed by other mobs in those areas. I haven't tested to see if the Y range is any different, but at y0 I was seeing slimes spawn in my test world. Looks like we will have to put a lot more effort into lighting things up with this datapack in order to get decent spawn rates.

I just copy pasted the code as it is here, and still only get bone_meal when using the composter [using 1.15.2]. It will drop dirt when broken while full, which was previously mentioned. So I guess the question is, should the loot_table apply only when the composter is broken, or also when it is used? [attached is the test datapack I used in a clean world]

I'm fine with this as "expected behaviour" if it is  only for  when it is broken, this is not inconstant with drops for other blocks. In which case I'd like to request/suggest that composting be implemented the same as fishing where it can have it's own set of tables/actions under the loot_tables/gameplay tree, as this would bring it in-line with other components of the game.

No need, the bug, as usual, existed between the keyboard and the chair. I inadvertently had a second datapack installed that was interfering and causing this behaviour in my test world. Once I removed the offending datapack, the overrides are working as expected. Sorry for the erroneous report.

I've been working on this as well, and by no means an expert either. Having said that, best I can determine is that the block loot_table is for when the block is broken, not for when it is used. So in this case you are setting what happens when you break the composter. I have tested and confirmed this to work, under the scenario of breaking the composter. I think this is expected behaviour, and not a bug. To change teh behaviour of the composter when used, requires a bit more work than changing the loot_table.