I am having the same problem and to be honest it's driving me crazy! here's a rundown of my issue!
1. I have done auto trim on all channels to make sure the gain input is ok!
2. Auto Trim is turned off on all channels
I do live sound at a church and we decided for these setup for it's technology and convenience!
While musicians are performing live the volume drastically drops to a point I have to increase the output levels.
After a while the volume will come back to normal which forces me to reduce the output level
This happens without notice and I need to be monitoring very carefully! It is a shame that after many hours of working and tuning my setup presets and gain levels I can't just sit an mix without stress!!!!
we are at the point of looking into another solution as this one is not performing as expected!
We hava a Yamaha mixer that does not have this issue so I know all my cables, Power amp, speakers etc work!!!
Any ideas or clues???
Thanks in advance