Thanks for taking the time to reply Saltgrass (never heard back from Dell support...).
It constantly failed over WiFi (fast connection, no other devices connected when I tried to update just in case) - all other security updates went on without issue. Purchased a USB to Ethernet adapter and connected it directly over our gigabit switch. Took about an hour including reboots and all now seems stable. I suspect the Killer WiFi may have been dropping the connection, need to investigate more when I have time.
Will also download the iso/USB install from MS just as a backup too.
Best wishes 🙂