@Matt Dillon,Thanks for posting in Q&A.
We are glad to know that you have found out the problem. Please allow me to give a brief summary of this problem to help people with the same problem.
Issue Description:
Rename Admin Account got issue using pre-provisioned Autopilot deployment mode.
Resolution:
From your description, we know that the issue of renaming administrators occurs in Autopilot pre-provisioned deployment mode; to solve this issue, it is recommended use User-Driven mode.
Thanks for your time and have a nice day!
Or you can open an online case to get deep dive Autopilot pre-provisioned.
https://learn.microsoft.com/en-us/mem/get-support
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