Only affects migrated accounts
When a previously migrated user changes their name, the previous name of that user should be dropping to the public after the 37 days "grace period", but with migrated accounts this does not happen. After 37 days, this name is unclaimed, and still assigned to the UUID of the previous owner of that name.
Links that proof this happening to "otu":
https://api.mojang.com/user/profiles/0ef953451e4846458e842f137bf25dc1/names
https://api.mojang.com/user/profile/agent/minecraft/name/otu
https://api.mojang.com/user/profile/0ef953451e4846458e842f137bf25dc1
This is currently happening with a lot of names that should be dropping to the public soon, and creating "blocked" usernames because they are not claimable.
Linked issues
Comments 2
This was never really a bug, we did it intentionally to allow players to reclaim their name they had before migrating due to WEB-5087. In any case, this is now "fixed" and we've opened up to claim names that were owned before migrating.
In my opinion, this should be marked as high priority. This has affected a lot of accounts at this point.