Hi Matt, Thanks for posting here in the Microsoft community, it sounds stressful especially since your other PCs don’t have this issue. Since you've already done clean installs, it might be worth checking if something like a faulty TPM, misconfigured Secure Boot, or a third-party cleanup tool is wiping your credentials on reboot. Also, try creating a new local user profile to rule out profile-specific issues.
What you can try, Check Credential Manager, ensure credentials are being saved properly. Corruption here could cause sign-in data loss.
Next, Review Group Policy or Registry Settings, look for policies that might clear credentials or user sessions on reboot.
Also, Check TPM & Secure Boot, If the Trusted Platform Module (TPM) is malfunctioning or Secure Boot is misconfigured, it might prevent credentials from persisting.
You can try also, create a New Local Profile, Test if the issue persists with a fresh local user account to rule out profile corruption.
Also, Check for Third-Party Cleanup Tools, some security or privacy tools may clear saved sessions on reboot.
To better understand, have you checked if Credential Manager retains your saved credentials after a reboot, or are they being wiped as well?
Let me know how it goes.
Chard