Hi,
are you talking about the shortcut “S” in the project window? Here it will always refer to the latest track you have recently put your focus on in the left zone, no matter if you have put the focus on a midi or audio clip from another track in the project window itself. In order to solo the track you want to solo you need to put the focus on the track in the left zone.
Just a thought, who knows… Sometimes it is that simple…
Normally, the S key command soloes the selected track(s) and also its/their associated group track(s), if there are some. Additionaly, if you select a return channel of a VSTi set as an instrument rack, it will also solo the associated MIDI track. IOW, the solo command also takes account of the routing setting of a given track.
As often, and considering the behavior you describe, I think that you are for a Cubase relaunch in safe mode, using the Disable program preferences option…
You wrote that you experienced this behaviour even after reinstalling Cubase. I guess you propably have other Cubase versions on your Mac as you have worked with Cubase since version 3. It might be that there are still user preferences on your system that are flawed. Take a look at this thread, the latest approach aims at corrupted preference files:
So, my suggestion would be to search for all user preferences and temporaily rename the folders before restarting. But that is just a guess to rule out all potential triggers for that annoying behaviour… I understand that it is impossible to worh with a bug like this!
According to the info I got on the forum, there is no file specifically named Cubase/ User Preferences. I’ve received no answer to what files I should specifically delete.