Ok, and now it's stopped showing up in the "arp -a" list at all. Tried swapping ethernet cables with no luck. I really don't want to stop the print as it's already been running for hours and it'll be a massive set-back. The print seems like it should continue all ok as it's running from the SD but I just don't like the idea of having no control. Also, I won't be able to retract at the end of the print as I have no control.
Hoping a power cycle will fix, otherwise I'm stumped.