After update to Moodle 3.5 (from 3.1) one course shows "Class 'Object' not found". I tried to deactivate all extra plugins, there are not many used anyway. (Lightbox Gallery, Bootstrap Elements, People Block, Notifications). Also other courses that are set up exactly the same way show fine and alle the plugins work.
What could cause an error "Class 'Object' not found" under these circumstances just in one course? Debugging set to on shows no further clue. PHP 7.1 is active PHP-version. Server is Ubuntu (Hosting)