Screen capture: Clip gain envelope is at 0 dB but tooltip shows the actual gain -INF.
 
I was moving tracks in a large project to make a medley of a live gig. After many (30-50 or more, one crash between) edits one track stopped playing back. I double checked that nothing was muted. Finally I found that it was the clip gain that was gone to -INF during move. By undoing move clip gain was restored to normal. I moved clip again and clip gain went to -INF.  All other moved clips (~30 tracks, 1 or more clips on each) are heathy but only this very one track has a reproducible problem. Maybe take lanes, I don't know yet.
 
Workaround: Clip gets alive when clip gain envelope is edited manually.