I have three instances of a VST track instrument in my project. On two of the instrument tracks when I solo them then Stereo Out is being muted, which is really unexpected. All three of the instrument tracks are being feed into a group channel track with its output to Stereo Out. When one of the problem tracks is soloed the group channel is also set to solo, but Stereo Out is muted.
Working in reverse, if I solo the channel track then only one of the three input tracks is set to solo. I would expect all three input tracks to be soloed also.
Looking at the routing for the instruments they are all VST → Group Channel → Stereo Out.