I've been trying to figure out why my puddle slimes keep disappearing from my ponds, and believe I have figured it out.
Posting here because it seems to be a bug that's easy to duplicate.
If you have a puddle slime in your pond, and shoot water at it - it leaves behind the same "slime splatter" as slimes on land leave when hit with something. Note the two blue patches in the pic below.
This seems to fool the game into thinking the slime is on land, not in the pond.. and start the same timer as if it was thrown on land. Seconds later, it disappears... even though it is in the water (pond).
I'll post specs if needed but this doesn't seem to be an issue on my end?