Encountered this bug when making a villager breeder; I have a 9x9 area of tilled soil next to two areas, one for the farmers and one for the baby villager beds. The baby villager area is separated from the tilled soil by a 1-wide, 2-deep gap, with water at the bottom. The gap is bridged by open trapdoors. Above the trapdoors is 1 block of air, then a top slab, creating a 1.5 block high gap for baby villagers to walk through, dropping them through into the water. The entire area is walled, the only way into the baby villager area is over the trapdoors. 

The bug; the baby villagers do not pathfind to the beds, and the frustrated/link breaking affect appears at night when they try to sleep. Replacing the trapdoors with solid blocks does not fix the issue. Removing the slabs, however, allows them to pathfind, so the trapdoors are not the issue, and replacing the tilled soil with regular dirt also allows the pathfinding to work properly. Perhaps they see the step up from tilled dirt to a solid block as a full block of height difference, which would make them think it was only a half-block of room?