in ProTools when a plugin has different numbers of input and output channels, the bus is muted and will not come back, even when removing the plugin from the track and also not when closing and reopening the session.
To reproduce I created an empty plugin compiled for AAX, opened a session, created a track, added a signal generator -> the mixer meter shows output and I hear the signal.
When I now add the Plugin Stereo to Stereo, everething is fine, but when I add the Plugin as Stereo to 5.1, the meter shows no output and the sound is gone. What is more strange, when I now remove the plugin from the insert, the bus is still dead.
Next observation, when I now reopen the session, the track is fine again, but when I saved the session before (without the defect plugin!) and reopen it, the track remains dead.
I didn't add a line of code to the new plugin template, also not the deprecated channel layouts, only switched to C++11, compiled with XCode 7.2, used ProTools 3rd party 12.2.1 build 41.
It used to work in that configuration before the multi bus feature was introduced.
Please have a look, thanks