Hi All,
I also had the issue with the headphone and left main output loosing signal. It would require jiggling the cable until eventually it would work. As this isn't the ideal solution, and because I am no longer under warranty, I decided to open up the Stagescape. The input section of the mixer encompasses the XLR inputs and outputs direct mounted to two circuit boards. Not much to go wrong here short of faulty solder joints which seem unlikely. While I had it apart, I removed and re-seated the ribbon connectors from the input/ output circuit boards to the main logic board, and lo and behold, this fixed the problem! This was about 3 months, and a dozen gigs ago, and I have not had a problem since. Not sure if this will work for all, but wanted to share my experience.
I also agree with others on this board, I love this mixer, and it's a shame that the quality control issues can't be resolved. I hope Yamaha commits to continuing the Stagescape line.