All files gone after closing and reopening SAB

Hi, I just built my first app and ran into the following problem: The app compiled fine and it works, but when I came back later to Scripture App Builder to add some more audio files, then all my books and previously loaded audio and timing files were all gone. Before I closed SAB, I had saved the project, but now when I open the project again, the books menu page in the apps tree view is empty.
I then created a new app for testing with only one file, and again, I saved the project. But the same thing happened. After exiting and reopening SAB, I can load the app project from the file menu, but the book is gone.
Does anyone know why this might be happening and how to fix it?

I should also add, that the books and timing files are all there in the project folder, but somehow when loading the *.appDef file into SAB none of these files show.

Did you have your .appdef file open in a text editor while you were working in SAB?

No, I didn’t. I opened it afterwards to see what was in it. Bun not while SAB was running.