Villagers will try to pathfind through solid walls in order to reach their POI blocks, resulting in them being stuck until their schedule allows them to switch to a different POI. This problem tends to plague custom villages with large structures. I've screenshotted an example village and diagrammed it below. This can be reproduced by creating a large chambered building with job sites and beds with a single or double door entrance and then spawning villagers.

MC-156031 can also be observed with this layout,