I noticed this bug back in version 1.14.4 but it is still on the newest version. The fact is that a resident priest is completely surrounded by a fence (3 blocks high), but somehow through this fence he can lie on the bed and thus escapes.
MC-172877
Villager can enter bed through fences
Resolved
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0
Please check if this is still an issue for you in 1.16 Release Candidate 1 or later.