I Have No Idea!

Just some F.Y.I. Ive been working on a session using Kontact NI session horns pro. Its been at least 4 problem free ones. Yesterday I open it and there is no sound but session shows signal. Im looking everywhere for I/O routing, mute/solo buttons, etc. after exhausting everything I could think of, I deleted the stereo inst track using kontact. Restarted session and Im back in business!? I have NO idea! Has never happened before. Imac 003