If you can't access files, then it means they're temporary lost. To recover them, start the application then go to Settings > Find/Recover Missing files. Wait for the application to finish the scanning procedure. You can then find the files in /mnt/sdcard/DCIM/recover
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This is the official way to recover the lost/deleted/corrupted files. For additional information contact the developer at the following email address: morrison.android.software@gmail.com