So we have implemented our side and Nitrado is working on their side. We are expecting to have Nitrado servers available in 1.3 😊 (though it's up to Nitrado right now, but the feedback we're getting from them sounds very promising 😁).
But before you do, could you please try to get on to the broken server and after you do, send us the output_logs and output_logs_clean? You'll find them here: C:\Steam\steamapps\common\Ylands\Ylands_Data
We each have our own build style, I guess. The premade slabs are very limiting in my experience. And there are never the right piece you are looking for. No snapping to the world grid is a total PITA, and smooshing things together really isn't a thing.
Ylands has a different building mechanic. And as clunky as it is sometimes, it is still the best builder out their IMO. And I constantly look for good builders.
But Paralives may have them beat. I have high hopes.
Maybe try as a short-term fix to 'Save as' the project under a different name and then re-export it from the beginning. You can delete your old entry after that, so there isn't a duplicate. That should get rid of the error. But we're working on a proper fix.