When trying to migrate from a mojang account to a Microsoft account, if you have purchased a copy of minecraft with the Microsoft account it will not allow you to migrate even though it has not had an account migrated to it - if this is not a bug then the bug should be that there is no warning about this being an intended feature
Hello Ash, a Microsoft account can only hold one Minecraft profile, no matter if it's a profile that was migrated or purchased. If you attempt to migrate to a Microsoft account that already has a profile, you should be getting the error "This one is already taken" - is this not the case?