upgrading world from 1.17.1 to 21w44a results in structure spawning rules not being respected/retained, specifically, a witch hut converted into a farm pre-1.17.1 that has had the world migrated to newest alpha, 21w44a results in witches not spawning correctly within the bounding boxes of the original structures, and instead, general mob spawning occurs. May also occur in prior versions or be caused by a specific migration between versions. (initial world created pre 1.17.1, then migrated to 1.17.1 before converting into recent snapshot.)