Hi Jim,
If your HDD is faulty it may be putting the system infrequently into R/O mode, however you’d only be able to verify that via SSH or by plugging it into another machine and running a SMART check on it. It wouldn’t be impossible for that to be the case.
Once the NC Box is setup it essentially only uses the SD card to redirect the system to the HDD for boot.
Try a new image above, if it happens again I’d suggest looking to get it replaced under warranty.