FM2019 book: all links keep changing back to refer to a one and same file

Hello community! I have a problem with a .book file in FM2019. I have several different links on several different documents of the book and the links are supposed to refer to the other files in that same book. However, it seems that at some point while I'm working with the files they always change back to being this one and same link directing to the one and same file. Why does this happen and why changing and updating the links back to the files which they should lead to won't hold? Am I missing some point at which is shoul save the link changes or what? Or should I do something with the ditamap I made the book from and not with the book's fm files?

Update: it seems that if I update the book, the links do this.

Thanks for all the help and advice!