Issue: Problem when saving modified articles

I use two Namespaces, on the one hand ...-FAQ on the other hand ...-Wiki. If I edit an FAQ-article (which is chapter of a book) and save it, a new article is created in the Wiki-Namespace in which the changes are then available. In the original FAQ-article, they are not there.
Creating a new article in the FAQ-Namespace works flawlessly. Similarly, the change of articles in the Wiki-Namespace works with no problems.
What could be the reason?

Greetings
Storyteller