Chickens teleporting / escaping (Bug)

Chickens somehow 'teleport' or 'escape' enclosures from which they are kept in.

How/When it happens: If I travel far from the chicken enclosure (like multiple chunks), when I return to the chunk of the chicken enclosure, they will be spawned outside.

How/When it happens: If I start my game fresh and load into the chunk where the chicken enclosure exists, they will be mysteriously outside the enclosure.

Where:

1. They escape a 6x6 wooden fence enclosure. Until the bug started happening (began a few weeks ago), the chickens would remain in the enclosure permanent.
2. They escape a 1-block air contained space in an "automatic chicken cooker."

Results:
The chickens will be running around in large numbers outside the enclosure, with only a few (or none) remaining inside the enclosure.

Apparently the chickens will escape any enclosure regardless of size, and seem to know the difference of 'inside' and 'escaped' clearly.

My theory: is that 'reloading' a chunk, either from joining the world, or traveling far and returning to the chunk, is when the bug seems happen...

Also, whether or not this has any relevance, the world is: 'Converted from Xbox One, Peaceful, Survival, Achievements enabled, on a Realm.'

I have never actually 'seen' the chickens escape, they are typically outside the enclosure when I arrive...

Thank you!