Please open the app, slide to the 3rd page and press Setting. There is a "Find Lost Files" item in "Other" section. Have a try. If files can not be found back, please tell us some information in detail
1. What brand phone do you use? Some phone will clear residue data after you uninstall APP. Once being cleared you will not find it back if you didn't sync to cloud or backup.
2. Try to add some files that are not important again and uninstall it. And notice if any dialog box to clear the book appears then reinstall GalleryVault and See if the previous file is still.
3. Have you formatted your device or use any clean tool? Once do this to clear the date, you will not find it back if you didn't sync to cloud or backup.