Hi
I had the same problem. I used a XX book for Bible stories and did a back translation with the interlinearizer in Paratext 8. But then in Paratext 9, I couldn’t use it any longer.
I was then told the developer assumed that no verse numbers are needed in these Bible Module books and they disable the possibility to change to another verse number in the interlinearizer.
What you could do is to create a back translation project based on your main project and with the same verse numbers. You can then type your word by word back translation to this project. This is less convenient than using the interlinearizer but would be a way to still use the spelling dictionary and other checking options Paratext is offering.