Villager breeders and iron farms that use beds. Villagers are are standing right next to enough beds, but lose their connection to the beds, causing problems for the farm function.

Gnembon has this video showing the path finding issues, says it is fixed in 1.14.4, but we are experiencing it on my server with an iron farm – the villagers are surrounded by beds but don't sleep.

https://www.youtube.com/watch?v=xmFdOhTA7sY&feature=youtu.be