Intermittent problem with no sound except from Effects block

For about six months I've been having a very frustrating, intermittent problem - all of a sudden, the sound will completely drop out, except from the Effects section. If I turn off the Effects, I get no sound at all. It is independent of the rig - changing rigs does not help.

Today, I was playing for several hours with no problems, then put the guitar on the rack to grab a coffee, and when I came back the sound was gone. I literally did not touch the profiler.

I have not found a reliable way to get the box back to normal. I have so far not had to reset to factory settings, but right now the problem has persisted, and my usual tricks of power cycling, unplugging all cables and cycling, etc. have not brought me any relief.

I believe this started somewhere around OS 5.1 or 5.2, where it happened with alarming frequency. After upgrading to the 5.3.1 beta things seemed more stable, but the problem reappeared. I therefore upgraded to the 5.4.0 beta, and it was good until today. In fact, flashing the 5.4.0 image cured the 5.3.1 problem for me. I hoped the same trick would work today, but upgrading to the 5.4.1 beta has not given me any joy unfortunately.

I've read a couple of forum posts that seem like they might be related, but haven't found any insight in them:
Intermittent Output Dropout Affecting Main and Monitor Outputs
Kemper sends out only wet signal, no dry signal

The problem is fortunately very intermittent, but I'm dreading this happening during a gig - I have no reliable way to get the profiler back into a usable state...

Just to reiterate - this isn't due to some setting I changed. The box plays fine one minute, and the next - only Effects. The only commonality I can think of is that it has happened once when I plugged in aux input, and just now when I put the guitar down (perhaps I banged a pickup or caused a loud signal brushing strings?). So perhaps it has to do with a surge, or an electrical event or something?

Any ideas much appreciated!

Quote from hjscheffler

if the dry portion of the signal completely disappears it could be due to a phase problem caused by a faulty cable that connect the main outputs to your external gear (monitors, mixing board)
Are you getting the same problem also on the headphones?

I actually notice the problem primarily on the headphones, when I'm at home practising. I have had it happen in the rehearsal room though, where the effect was apparent on both the main output and the monitor output. I've also had it on the S/PDIF output into Logic, as I was trying to record the sound.

This time, the problem was still there overnight after I started the Kemper in the morning. However, as I was trying to check the other outputs, the problem disappeared:

- I plugged stereo headphones into the monitor output - didn't hear anything (normally I would hear something)
- Plugged 'phones into the main output left output (unbalanced) - heard the correct sound
- Plugged back into the front headphone output - problem was resolved

The box is now working normally - until the next time...

Quote from hjscheffler

What is the output source setting for the outputs that you are using to monitor the signal?

Main Output <- Master Stereo
Monitor Output <- Master Mono
Direct Output <- Git+Processing
SPDIF Output <- Master Stereo

I've also filed a support request with Kemper: Ticket ##KA00143721