Unable to Import repos (with History) from TFS / Azure DevOps

Hi all,

I am trying to import my TFS / Azure DevOps repos (with History) to GitHub.
These repos are all Private.

But every attempt to import is met with a login dialog with this message:

Your old project requires credentials for read-only access.
We will only temporarily store them for importing.

That dialog repeats every time I enter the credentials.

Looking through the security logs there are lots of events like:
Blocked a merge setting on the xxxx repository