Do the software reset at the device, there is no way to do so at the Web interface (CWIS)
Since it is a Connectkey product, you may be able to recover it by simply updating the firmware, what version you would go to would depend on the version you have now.
For now just make an entirely separate folder for their scans.
The old folder is likely corrupt and not recoverable, but it can't hurt to try accessing it with various methods, browsers etc.
You didn't bother with a model number so there are no specifics, if it is a bigger model it likely has a Software reset in the Troubleshooting location when logged in as admin, give that a go.
I am currently having an issue where a user has scanned documents to a private folder and had confirmation the scan is complete.
But when logging on to the printer and selecting the folder, inputting the password, the folder is not showing any of the files.
I dont want to recreate this folder by deleting and making new as there are around 200/300 scanned documents in there
Any help/advice much appreciated.