After an OS software update, my Mac restarts without my login keychain authentication, logging me out of everything the keychain is responsible for authenticating.

Almost every time my mac runs an OS update while it's sleeping, it seems to restart itself—meaning it reopens all apps in the background—but when I log back in, the login keychain has not been authenticated and so all services that rely on that keychain for authentication (primarily synced services w/ Apple, Google, Facebook, etc.) are logged out and require manual reauthentication (reentering passwords, including 2FA, for all of them).

My login keychain password is the same as my account password so I'm not sure why this is happening. Any ideas on how I can get it to stop restarting in the background without login authentication? This only happens if it updates overnight or when I'm not at my computer to sign into my account right after an update.

This has been happening for at least the last half year and probably longer. Because it's semi-intermittent, it's not a huge problem, but it's been going on long enough that it's noticeable and annoying.

OS 10.13.3 (17D102)