The issue you are having is that it is encrypting when otherwise restarting overnight wouldn't be an issue.
The part about auto restart is part of your problem, but your main issue (causing the encryption) is called "secure startup."
It makes you put in your password before it will start up to prevent someone from taking your personal info if your phone gets stolen.
As stated, you can shut off auto restart but this will still happen if it restarts for another reason (such as a software update) or you can shut off secure startup if you don't need it.
Find it in biometrics and security in your main settings screen.