Nextcloud resetted config.php on its own

For some reason my nextcloud installation resetted its config.php leaving me with just a default one:
$CONFIG = array (
‘instanceid’ => ‘ocnb1ijzw9hg’,

This is obviously a serious bug which should be fixed. But more importantly: How can I recover from this without a complete reinstallation?

Without more information about your system, the NC Version pp, nobody will be able to help you.

Why don’t you just restore the config.php from your backup?

Why do you think nextcloud has resettet the config.php?
Did you check your harddisk for errors?