Main Cloud Backup is showing incorrect dates - default to 1st Jan 1970

The first cloud backup I ran (which was of selected folders on one drive) has worked fine and shows the correct dates.

Now I am running a full backup (although only of the main hard drive (multiple paritions), because I have two additional disks which are just offline backups so I don't need them in the cloud). Backup is still running, but on checking the dashboard, the backups are shown as having run on 1st Jan 1970 - no doubt this is the default zero date for the code, but the question is why is it not showing the correct date? See screenshot attached