If a job site block has another block on top of it, villagers will claim it but will not be able to pathfind to it and therefore will not use it to restock.
How to Replicate.
1. place a job site block
2. place a block on top of the job site.
3. spawn a villager nearby.
As demonstrated below, the villager will claim the job site but will not pathfind to it or restock until the block above is broken.
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It's most likely not supposed to be like that, considering many of the job sites for armorers and butchers naturally generate with a block on top of them,

Please check if this is still an issue for you in 1.16 Release Candidate 1 or later.
This is indeed still an issue. Whenever a job site block has a block on top of it, villagers are unable to pathfind to it for some reason.
In the screenshots posted, the villagers have jobs.
This is only a problem in some instances.
see MC-199515
This is a duplicate of MC-199515. In this instance, it occurred with a villager that already had the corresponding profession locked in.
It is supposed to be like that.