Normally, I'd remind in the mobile sub-forum, but that's sort of who-knows at any given time. This problem's been around a while now, and previously reported.
If you're off-line, reading a downloaded book, and click on a reference for another book not downloaded:
- Program opens a blank panel
- Discovers the obvious (can't retrieve)
- Presents a completely blank screen to the user
- User must recover by removing the app from memory and re-starting (can't bring up menus)
Now, the normal design is to first check availability, then open a panel. Don't just blunder forward, hoping for the best.
A variation avoids the lock-up part. If you select the reference (for a book unavailable) while the top/bottom menus are showing, the user can recover without removing the app, and re-starting. Which highlights why a click on a blank panel can't bring up the menu bars.
Example:
1. Below, reading Lost Apocrypha, wanting to see where Jerome's Hebrew book is located (reference center of page)

2. Clicking on '4.17' opens a new blank panel, tries to load Targum Chronicles (which is incorrectly tagged), fails, and presents a blank screen (it's below .... really):

3. Clicking this blank screen does nothing. No menu bars, etc. Must re-start app to recover.
4. Menu bars DO appear, only if they were showing, when initially the ref is clicked.
And finally, in hopeless desperation, you highlight 'Hebrew Questions on Chronicles' to do a search ... it assigns the Apocalypse of James! Wooo-hoo ... go figure THAT out!