Edit I am reliably informed that:-
Sandbox uses its own Windows Local Account password, which I do not know. Without knowing the password, I don't know how to change it.
You can sign-in with a Microsoft Account in some places, but not in others. Places that require you to confirm using the Local Account password of course do not work.
Is this correct? If it is why have we not been informed when the app was flighted? If it is not correct what do we do?
David Elliott-
Windows Sandbox logs in under the WDAGUtilityAccount. If you check out the Hyper-V-Compute event log on the host system, you can see the account is created with a "net user" command line and the password is in plaintext (Create process, parameters '{"CommandLine":"net user WDAGUtilityAccount pw123","User":"NT AUTHORITY\\SYSTEM","ConsoleSize":[0,0]}', result 0x00000000, process ID 2468). You can see the password "pw123" is the password for the user account. I'm assuming that is just a hard-coded value because that doesn't look randomly generated to me. I verified the password works in my Sandbox by simply locking the Sandbox and unlocking.