Unfortunately I am not very familiar with those COM interfaces, but I think the JUCE VST3 wrapper fails to increment the reference count on that host smartpointer. I think I found the bug and it appears to be in the JUCE VST3 wrapper. Has anyone else seen that and maybe found a workaround? It’s also curious that this does not happen when inserting the same plugin on the master section. My conclusion is that the problem is either in Juce or Wavelab - my feeling is that Wavelab is to blame as otherwise we’d see the same issue in more vst3 hosts. To reproduce, load two audio files into Wavelab, create a Montage, insert a juce-built vst3 plugin on both tracks. Then I switched to the Juce GainPlugin demo and without any changes to any code, the exact same crash happens.

Thankfully, Wavelab allows attaching the XCode debugger. After a few attempts I managed to recreate the crash on my own machine using a debug build. He contacted Steinberg about this and they blame my plugin for the problem (naturally). I have a customer who gets a crash on quitting Wavelab 10.0.30 on OS X if multiple vst3 instances of my plugin is inserted when doing a montage session.