I have a theory that what’s really happening here is the track is actually just muted, but Cubase isn’t showing that it’s muted. If you run into this, try hitting mute on that track and then unmute the track.
I was able to fix the issue on a couple instrument tracks that I’d previously disabled. When I re-enabled them, they wouldn’t play unless soloed. Then I hit mute on the problem track, then unmute, and there was the sound. For me it worked on Kontakt and Omnisphere tracks where this had happened.
If that doesn’t clear up the issue for you, another solution I found from an older thread suggested adding a new MIDI track right below the problem track. This worked for me as well. Add the MIDI track and then the problem track works again. Then you can delete the new MIDI track.