Mojang Account Migration Failure

Okay the issue seems to have resolved itself and I can get in. What maybe the case is the migration is not as instantaneous as we would like it be and it is best to wait a day or two... especially if you are getting extremely frustrated.

I'm Samy an independent advisor and I'll be helping you

How are you?
Follow these steps and see if it helps you.

You have hit the button to go back to the accounts page. But then, don't click on your existing account that you want to sign into or you will just get back into the same problem loop that won't let you sign in. You have to add a new account. It is counterintuitive because you are not actually setting up a new account. But once you click to add a new account you can choose to sign in with your Microsoft account in the Launcher. Once you do that, it will automatically use the Microsoft account to log you in from the Launcher.

This is the exact same issue I am having. I've migrated my account like they say to do, have the emails confirming the migration and logged back in using my Microsoft account yet once I'm in it says I don't own the game despite having an email confirming that I purchased the game back in 2019. It even prompted me to log into the Mojang account to be able to play the full game but just like with you when I click and try to sign back into my Mojang account it says that I no longer can access the account as it's been migrated.

I contacted Mojang support yesterday but they just told me how to log in, to not use a 3rd party Launcher and to contact Microsoft for help. Microsoft says the same thing and then I'm stuck in a loop going nowhere and a missing game.

I hope they'll be able to figure this out as this doesn't seem to be an issue of "wrong email" or "account not migrated" like they seem to think cause I don't think it's right that I have to purchase the game again despite playing it the previous day before migrating.

Thank you Sam but that is what I am doing... I'm attaching my already existing Microsoft accounts to Minecraft and both of the accounts are telling me that they do not have the game. After I migrated my Mojang account to the Microsoft account using the same email. After I Migrated my Mojang account I followed the instructions to press the "< go back" prompt and I did then sign in using the Microsoft account not the Mojang one which I did and I successfully signed on but I can't do anything because the account is telling me that I don't own the game. I however did Migrate and even got the confirmation email on that email as well.

Something of note is that when I signed in on my Microsoft accounts I am being prompted to change accounts to my Mojang account to play the full game when I've already migrated and cannot access the account because it is supposed to be combined with the account signed in with.

Got it. In that case you should talk to Mojang directly to find out what happened with your account migration