I have a Chemist on a village. I've traded with them to lock their job, zombified and cured them, took them away to a new village using boats. I gave them available brewing stand job sites, but they never took it. They just wander around aimlessly. They took the new beds I provided, but never the job sites, even after breaking and replacing.

I also have a Librarian with the same origins. After moving them to the new village, they took their job site for a while, but after a few days, they stopped working and decided to wander around aimlessly. It could be because they unlinked from their job site due to getting stuck, but they never bother to seek out that same job site again, or other available job sites. Perhaps they didn't unlink properly? Their behavior is similar to unemployed villagers.

This new village is a big one with 30+ villagers, but I made sure that the provided job sites are new and available. Other villagers in my village are working as intended with their respective job sites. It seems that for some villagers, they just gave up searching for job sites.

Update: this still happens on the latest version, but I've found a fix. If I restart the Minecraft app, those villagers will attempt to seek job sites again. And if they unlink from the job site, they may never attempt to find job sites again, unless I restart the app again. My village is at 50+ villagers now, and this behavior seems to mostly happen on newer villagers that I've taken from another village (after zombifying and curing). Most of the other villagers are working as intended, and will seek new job sites if they unlink.