I am stuck on this issue as well. In my case, I believe f-stop was interrupted during an initial scan of around 30,000 images on the sd card. Now I can only successfully search for metadata on the images that were processed before the interruption.

I am also hesitant to uninstall/reinstall f-stop due to previous comments about Android clearing out the /Android/data/com.fstop.photo folder on the SD card on uninstall.

Any updates from the developers? Please? 🙂