App-specific password fails on MacBook Air after shutdown

Reset your Login Keychain (most reliable)

If the login.keychain file is damaged — this is common on Big Sur — it will not unlock early enough during boot.

Steps:

1. Open Keychain Access
2. Click File → New Keychain…
3. Name it login (this replaces the old login keychain)
4. Set a password that matches your Mac login password
5. Reboot
6. Re-enter your app-specific password in your email or app settings

Now the keychain loads cleanly at boot, and the password persists across shutdowns.