New activity title isn't rendered, the filter process never finishes

Detected by isabelrenedo in the Moodle App, I'm opening it in Open Source project to investigate it.

What she did is:

1. Access a course in the app and leave (so the data is cached).
2. In LMS, add a new activity in the course (a URL resource).
3. In the app, download the course.
4. Go offline and open the course. The new activity's title isn't rendered, it displays the grey area that is displayed while the filters are being processed.