For tracks monitoring incoming signals from outboard, Solo Defeating those tracks does not prevent them being muted when another track is soloed. In other words, the monitored signal does not pass through even though they are set to Solo Defeat.
Is this by design?
Why?
It’s not the case, here, unless I didn’t get the issue (the four first tracks have the same MIDI port as input and are getting notes on the same channel) :
Thank you for confirming this is not the case normally…I’ll have to dig further and see where I’ve botched it.
OK, in my case, I needed to Solo Defeat the main Stereo Out output track as well.
Hi again, @zooterman
I never had to do so, actually. Using the Solo Defeat function on the involved track alone has always worked flawlessly. 
Hmmm ok, probably because my main stereo output bus is “not connected” and instead I monitor exclusively through the control room monitor connection. That’s the only thing I can think of right now, since the solo defeated track was connected to the stereo main out bus.
I also use the Control room with, as you, the Stereo Out bus set as “Not connected” in the Studio > Audio Connections > Outputs panel. So, the issue is somewhere else, IMO… 
Thanks for confirming that.
I don’t know then! But it’s working with stereo main out solo defeated as well.
OK. If I find something on my end that could explain the issue, Ii’ll let you know here… 
Thanks.
The other thing is might be is my monitor-enabled tracks are monitoring an incoming outboard signal, whereas in your example the tracks are internal VSTi’s. I’ll test if that makes a difference when I can.
It still wouldn’t make sense, but it could be a software quirk. Probably not it though.
Can you provide a screot of the tracklist? That we can see what it looks like?
To be honest, with reference to this scenario in the screenshot, I can’t see how you would be able to hear anything without also solo-defeating the main stereo out bus track. Because as you can see, if it is not solo-defeated, Cubase mutes it.
Just to avoid any confusion, STEREO MON track above monitors the incoming signal of a hardware synth.
Is Audio1 routed to the Stereo Out?
No it is not.
And I think you’ve landed on an important point… Because the main output bus would then not be muted.
So the specific scenario is, if a track routed to a different destination than the main output bus is soloed, the main output bus will be muted.
So for applications like soloing an audio track that is routed through outboard processors, you won’t be able to monitor the return through Cubase unless the main output bus is solo defeated.
Thank you! I had this exact same issue and never would’ve found that solution on my own. I thought I was crazy. Solo defeating the master bus worked for me as well.
I’m sure you are aware that this must be working like this.
If a signal is routed to a different output, the master output is not involved in any possible signal flow with this output. So it can’t be used for soloing, since solo is a solution that quickly mutes all signals except the soloed signals. If the soloed signals are not routed to the main bus, the main bus must remain muted.
And it is not like a PFL bus on a mixing desk, to get similar functionality, you need to use the listen bus or as you already know, switch the master bus solo defeat.
Not if you use the external fx and set it as an insert on a bus or channel, that is routed to the master. It behaves like an inserted plugin then.
