Tomtom Rider 400 won't recover
The answer I ultimately received was that there was a download problem due to security issues.
I replied that this is not the case as when all security and vpn is turned off MyDrive sits for hours 'Busy repairing your device' which it doesn't do. There's been no further help on this.
To reiterate - downloads work ok into the cache then nothing useful. When looking at the process it seems MyDrive doesn't read from the cache or write to the device but does the following shown in the image.