In my server i have noticed that mobs do not spawn like they used to do. Me and my friends always start a server every year on the newest version and we try to beat the game and kill the ender dragon. We have rules and one of the rule is that you can use websites to locate slime chunks. I always build every possible farm/auto farm when i can. So i built alot of farms like food, animal, xp, slime, sugar cane, cocoa beans farms. And i noticed that the farms that contain mobs (xp farm, slime farm.) Doesn't work. The mobs just dont spawn. I know i built those farms corectly because i found the slime chunk and i know that it works because 2 slimes spawned there. But only two and then they just stopped spawning. The same is with my xp farm, I go to my xp farm and a mob spawns every 5 minutes.