We have the same problem, which is quite frustrating.
i created a B2C domain on side of our Azure active directory for testing. at this B2C domain i am the only admin and user , also domain is with MFA active. By switching Phone i lost Authedicator App. Now i cannot log in to this Domain. it's OK. but I can log in to the my Azure active directory no problem at all.
But huge problem is at on Visual Studio, when i want to connect a service from Azure, always ask me the MFA by logging, but i do not have any MFA on my orginal Azure Active Directory, always link to the B2C domain MFA, very frustrating.
I do not need to logging with B2C domain, any Suggestion instead of Ticket!?