Got impatient and ended up using chat support - not very helpful but they are working on it which is good news!
"At this time, our development team are still working and is aware of this" Apparently it is happening for a lot of stores, no estimate for time to be fixed but hopefully less than 24 hours since it's a widespread issue.
In the exact same position! Stock arrived late yesterday and only half made it online intending to launch tonight but seems unlikely now.
On the plus side they did say if the issue wasn't resolved in 24 hours they would look at refunds or compensation due to lost revenue from being unable to list new products. Fingers crossed it is fixed soon though!