Hello
I understand your concern about the Windows 11 sign-in setting changing randomly. This seems to be a known issue. Here are a few things you can try:
Check for Updates: Make sure your Windows 11 is up to date. Microsoft frequently releases updates that fix known issues.
Sign-in Options: Go to Start > Settings > Accounts > Sign-in options. Make sure the setting “If you’ve been away, when should Windows require you to sign in again?” is set to "When the PC wakes up from sleep".
Dynamic Lock: Check if the Dynamic Lock feature is enabled. You can find this in Settings > Accounts > Sign-in options > Dynamic Lock.