The bug

As of 1.14.1-pre1, villagers are unable to take the profession of any profession block that they can't reach. As you can see in the screenshots below, when villagers have no path to a profession block (such as when they are trapped with a fence between them and the profession block), they won't take on the profession of the block and will stay unemployed. However, as soon as a path is made available that gives them access to the profession block, they immediately recognize it and take on that profession.

I believe the intended behavior is that villagers should recognize all POIs within a village, whether or not they have a valid path to reach them. This was the behavior in 1.14, and it would allow for players to more efficiently contain villagers and sort villagers for useful trades.

How to reproduce

1. Spawn a villager that is surrounded by fences (or trapped on a floating island, etc., just somewhere with a barrier that keeps it from escaping)
2. Place any profession block outside of the fence / on the other side of the barrier / in the air where the villager can't reach it