This is a strange one I can't seem to figure out. This is my PC running Windows 10 Education edition.
I connected to my university's Azure AD last year, and created a local profile from the student e-mail address.
During that time I had logged into a second account (for personal use i.e. gaming) which is linked to a microsoft account.
Today I wanted to create a local account to personalise another desktop for a specific type of work.
Upon creation Trying to switch that user will show a wrong username / password. Attempting to type "\username" results in the error "You can't sign in with a user ID in this format. Try using your email address instead.
I would remove myself from the AzureAD, however my main account is tied into it.
Things I've tried:
Filtering out any changed settings in Group policy that would effect it
Viewing Regedit changes
Advanced User settings to change the account to local