From Han Wiki

Fixing integrity check error

When you log into your instance of ownCloud you can sometimes see, "There were problems with the code integrity check." Whether it's by a new file you've created, or a file that has gone out of sync, there is an effective way to get rid of this message. Make sure you know for sure the reason why these error is coming up. You do not want to wink at a trojan penetrating your system.

Here is how you can ignore those files from integrity check. You can insert something like this into your ./config/config.php file.

'integrity.excluded.files' => [

Then you run the following.

$ sudo -u www-data php occ integrity:check-core