Every day when the villagers are supposed to go to the meeting point, many will not.
It is often the villagers who are farther away, so it could be insufficient range for pathfinding.
To reproduce, go to any village and do /time set 8999, so that the villagers will proceed to the meeting point. This exposes the bug almost every time.
Seems to work for me, once you give them time to finish whatever they're doing