[CoursePress Pro] Changes in coursepress pro not saved

When I add lessons and/ or chapter the heading will not be saved and also not shown. Any idea?
It is a multisite installation. Coursepress pro only on this site activ.
Here is the link to the site in progress:
https://academy.docmoritz.net/kurs/wissenskontrolle-herz-kreislaufsystem/lektion/34 Where is written "ohne Titel" should be the chapter heading...