I created a hardcore world in a snapshot 20w16a, and I had built a large scale witch farm, slime farm, and guardian farm. (Listing the affected farms) I recently tried to afk in my guardian farm, and it would appear no guardians had started spawning. I went to my slime farm to try and get slime blocks, and no slimes would spawn. I have lit up every cave in a 500 block radius, and the mobcap is at 0. No mobs. I went to check on all my other farms, my natural regular mob farm (Zombies, Creepers, etc.) Would spawn mobs normally. My enderman farm would spawn mobs normally. My witch farm, did not spawn any witches. This looks to me that the mobs that are supposed to spawn in certain chunks or areas (Slime chunks, Witch Huts, Ocean Monuments) appear to not spawn, those mobs. I'm not sure what I can do at this point, I believe this is a different bug than the MC-148613 bug report. Please look at this asap, as it could be a large-scale bug.  I am open to downloading any world revives.