Agreed with @ryanb – also thanks so much for helping with this topic. We do appreciate having community driven help on these things as there’s not many of us with free time to fix everything.
For @null (nice handle 
) have you tried using the alpha version of nbconvert (6.0.0a1)? The change ryanb made is in that release and might help if you’ve got 5.6.1 install instead. We’re pushing on the last changes needed to do a full release of 6.0, but knowing if there’s gaps we should try to address before that finalizes would be good to capture.