New lesson not appearing immediately

I import a book into LINGQ. The system divides the book into lessons. I read on my iPad. When I finish a lesson and go to the next one, it happens regularly (but not always), that the text of the new lesson does not appear. I then have to close my iPad, open him again, open LINGQ, click on the lesson. Then the text appears, but there is also a pop-up saying:
App is offline. Showing cached lesson data. Refresh the lesson to see the latest version .
This is of course rather annoying. It did not happen in the past. Can anything be done about it?

usually the system needs some time to make all the lessons of a book ready to use. did you give it enough time?

Yes, the whole book was already imported weeks ago. Making the book ready to use is not the problem.

I see, we will look into this. thanks for your patience.

I’l have patience. But I will be glad when the problem is solved!