Unstable control loop

Traces from top to botton: output voltage, output current, over-current signal, combined voltage/over-current control signal going to the power transistor drivers.

I replaced C26 with 22pF. Doesn't work. I hope it will go back to normal when I put the old one back in. I think I will add a socket for further experiments. Maybe I can still tweak it with a trimmer-capacitor.