OK, so I tried again.
Re-listed my item from 10 days to 7 days, starting this evening;
Un-checked everything that might introduce script errors on Ebay.DE (scrolling, singing, dancing, galleries etc...)
Passed Auctiva error checks;
Failed to list - Script errors.
Luckily, I had prepared a backup:
I listed the same item via Ebay with a slightly later start time.
Listed fine - Guess I'll just let that one run.