New words not being saved properly

(OnePlus, Android 15, OxygenOS)

When I have blue words and add them so they become green, if I then close the lesson and reopen it, a lot of the words are not saved and I have to go back through the lesson and re-add the words.

I have had this issue since 6.0, it is not breaking the app of course but it is a bit annoying especially when importing an epub file for example with every lesson having 6000 words.

I was in contact with support about it back in July, but they were never able to reproduce it unfortunately. I took a break when my subscription ended in November, and started again two days ago but the issue is still here.

Is there anyone else who have had this issue? And did you find a solution?