Mobs get stuck on top of half blocks, whether or not they can collide with them (this in Minecraft Java Edition, version 1.14.1 Pre-Release 2):
Scenario 1: Natural occurrence.-
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These foxes attempt to catch the fish underwater, but get stuck on top of the kelp or sea grass.
Scenario 2: Provoked
[media]In this case, despite seemingly having a continuous path underneath them, the mob will spin in place in a failed attempt at finding the path to its target.
A similar issue of path-finding appears to occur with the villager getting stuck inside a space enclosed with open trapdoors. It most likely happens since it's not taking into account the new 'open' state the trapdoor is in, this since the villager is just pushing himself towards the edge of the trapdoor instead of jumping.
@violine1101
I see, I believe the filters I set to see if there was already an issue like mine were too limiting. Should I move that comment there or delete it, since the info I add is pretty much already covered there?