Posting on the forum as well. I have exchanged a few messages with Johan on PM.
I suspect that the backup have failed and thus the restore from this fails. We recently found an unpleasant bug in the USB mass storage backup that could be the cause of the corrupted backup.
If you use a VFAT formatted device, which most USB-sticks are by default, and the backup grows to a large size. The VFAT filesystem om the device runs out of file entries. I.e. you cant create more files on it even if there are storage. (The limit is in the range 32-64 thousands of files in a single directory.)
Currently the best way to avoid this is to use a Linux Ext4 formatted USB-device for backups.
Thankfully Johan still have the orginal OPI SD-card untouched. What we have recommended in his case is to do a downgrade of the OPI and redo the backup and then use the new backup with the Kinguard upgrade
Put support questions regarding OPI here. Examples are hardware related issues and other questions that are specific to OPI.