Hi Mark,
I was able to reproduce your issue.
We do seem to reach a usability limit (where the editor freezes and behaves very sluggishly) when you nest test plan references that deep.
Can you elaborate more on the modularizing aspect of what you are trying to do with so many levels of nested test plan references?
@rolf_madsen Maybe you can also chime in on whether there are any concrete usability limits to what Mark is trying to do here and if there is any alternate way?