I'm running into an issue with both a premise based setup and sandbox. Mx 6.1 is unable to create an MxAdmin account within the database (on newly created DB's). Sandbox Error: M2EE: An error occurred while executing action 'createadminuser' Premise Error: User/Account does not exist. This is preventing me from deploying to the sandbox, I was able to move forward with a premise based install by restoring a local copy of the Database (That already had an MxAdmin account) that was previously created with 6.0.1
I ran into the same problem, also on version 5.19.0 +.
What I did, was create an after start-up microflow, which would retrieve or create an "Administrator" account. Not the best way, but fine enough for my sandbox application.