I had an allay attached to a lead and completely fenced in, and somehow it escaped twice. My game is completely unmodified and never has been. The allay had been in here since one of the 1.20 snapshots as it was part of my pitcher plant farm, and never once got out until this week. At first I thought it was just a weird one-off thing, but it has now happened twice.

Attached are pictures of the enclosure.