Saved data is missing
Please do not delete the app. The videos and images you saved live inside the app's own storage on your device, and deleting the app removes them too. I cannot restore data that has been deleted.
1. Check these first
Is a filter or sort order hiding it?
Sometimes the data is still there and simply is not showing. Check the folder sort setting, and the image size filter in iDig. If you moved it into a binder (a folder inside a folder), it is one level down.
Look directly in the Files app
The apps expose their storage to the Files app. Open Files → On My iPhone → the app's name to see exactly what is still there. This works even when the app itself will not start. If your files are listed there, the data is safe and the problem is only in how the app displays it.
2. What to do, case by case
It disappeared after switching phones
Depending on how you transferred your iPhone, app data does not always come across. If you still have the old device, you can copy the files across yourself. On the old phone open Files → On My iPhone → the app's name, copy the folders somewhere else (iCloud Drive or a computer), then bring them into the new phone.
If the old device is gone and no backup restores it, there is unfortunately no way to get the files back. Everything you save stays on your own device — none of it is stored on my servers.
I deleted the app and installed it again
On iOS, deleting an app deletes its data with it, and reinstalling does not bring it back. Please avoid deleting the app when something goes wrong.
An empty folder is all that is left
When a download fails part-way, a folder can be created without any contents. The bug where such leftover folders could not be deleted is fixed. Check the release notes and update to the latest version.
I deleted it inside the app by mistake
There is no trash can in the app, so deleted items cannot be recovered. Deleting a folder asks for confirmation to prevent mistakes, but for anything important I recommend copying it out through the Files app.
3. If none of this helps
If you can open the app, write to me from Settings → About this app → Email a bug or request. Your iOS version, app version and device model come along automatically, so I can start looking into it right away. If the app will not open, please use the contact form.