Within my moodle system (version 3.3.1.+) it happens almost daily that under the path 'Website-Administration --> Plugins for authentification' the email-based self-registration deactivates automatically. The "eye" is then crossed out and the majority of user can not login anymore. In my opinion there seems to be no valid reason for that. 

Further, within the settings 'email-based' is selected as current setting. As I am the only admin I am also 100% sure that I have not deactivated the plugin myself.

In the Log-report also no errors are reported.