Just as you have an “unmute all tracks”, it would be highly convenient with an “unsolo all tracks”. Quite often, you solo a track, then need to add another track or two or three. When done editing, it would be best to have the option of un-solo’ing all tracks. It’s needed since you changed the “solo” function from muting all but selected track to actually solo that particular track.
The same options that applies for muting tracks should be available for solo’ing as well. Hope it’s possible.
Even more strangely is you Solo a Send (which Solos any Tracks feeding it.)
Then hit Solo again expecting to go back to everything normal.
This just takes the Send off Solo, leaving the source tracks which are quite likely silent as they are feeding the Send.
Guess I’ll just have to remember to hit Solo on Master to bring all back. Which will also do what you want 
I would also greatly appreciate a shortcut for un-solo’ing all tracks. I can remember that pushing ctrl-\ twice would unmute all tracks. Having that function back would really speed things up…
+1
There is an Unmute All Tracks available but not assigned to anything by default. Unfortunately it appears to only work on Mute states, not Solo. I think it should always bring back the desk to all tracks on (no Solo or Mute) rather than just clearing mutes.
Right clicking the Master track solo button solos everything so if you need to quickly clear all your solo’d tracks just double right click the master solo button.