Yeah that’s exactly what I saw in surge and then also in our juce plugin. The problem (short version) was that the VST3 api (as you know) as registerHandler( handler *, fd ) and unregisterHandler( handler ), but bitwig was making one handler and then multiplexing internally, so if you did something that registered a new handler transiently (like initialize another xcb or something) it would unregister the same handler as for the main xcb loop. I also had some bugs in surge which had us confused for a bit but once i got those fixed with reaper and your (super duper useful) audiopluginhost we found it.
I got the impression that 3.2 beta 4 will be out ‘shortly’ but I don’t have a date.
So now the only thing left for me releasing vst3s of all our juce plugins automatically from our CI pipeline is Building my VST3 with Linux and JUCE6 - couple of tiny things which I know @reuk is looking at. I am very excited!