whenever a creeper explodes on slime blocks, they stay there. They can't be interacted with. I do have mob griefing turned off. when i switch the game to peaceful mode, the creepers don't go away. I reloaded the world, and the creepers were gone. I tried to explode creepers on the slime blocks, but the bug didn't happen again. I tried this on another world and the bug didn't happen. This bug happened on the same world that is affected by MC-201217
EDIT: I was in that other world, and eventually another creeper and and spider froze, then this started to happen with a lot of other mobs. unlike MC-201217, new spawned mobs from a spawn egg don't freeze and are interactable. In the 3rd screenshot, there are 10 frozen creepers and some item that can't be picked up or killed.
This seems to be a lag problem. Lag problems are generally not considered a bug, unless there is a clear reason and solution.