Burning skeletons will attempt to put themselves out in waterlogged blocks, causing them to sort of run in circles in a particular spot.
i would also like to add if this bug is a duplicate, im sorry for wasting your time.
MC-135533
Skeletons see waterlogged blocks as water
Resolved
Duplicate
0
Adam Eason
(Unassigned)
Unconfirmed
Minecraft 1.13
Retrieved
They might actually be running to the water itself (not to the waterlogged wooden slabs), but get stuck on them due to MC-127149.