Well, that. I opened it up and felt a little scared because of the picture below. SMD parts!!

Luckily it only turned out to be a loose connection at one of the input jacks. The front jacks were loose  from the chassis, so from regular use it’s obvious that this would happen since the jacks are soldered to a PCB. I took my time and dressed the solders from all of the jacks, inputs and outputs. No more dropping of the signal.

Jack causing the problem.

View from the back.

Testing, testing! Yup, that was all. Simple, but time consuming getting it done!