Reflow means that You melt every soldered connection again, preferably with some additional good quality solder, it sounds like a classic cold solder joint problem.
Often associated with bath soldering components with varying thickness leads/legs.
If You don't want to do 'em all, start with the thickest legs, that's where the problem most likely lies.
It only takes quite a bit of Your time, so DIY is the only way, absolutely no point in
The DDT was (still is?) the protecting compressor Peavey uses, if it malfunctions as it IME pretty often did, it tends to cause all sorts of problems.
Back in the day when I still bothered with Peavey gear, we used simple "malfunctions" to simulate the circuits behaviour to find out whether it worked or not. If my failing memory doesn't trick me too much, the DDT circuit was pretty easy to defeat in CS series, but near impossible in some newer offerings from Peavey.
There's an (un)official Peavey rep on TB, he usually helps people who are in trouble wth their gear.
If only that kind of service and dedication to CS in general was available over here back in the day, Peavey might be considered to be better than Behringer.
Edit:Good to hear You figured it out while I was typing. Do replace the switch though, should be easy enough to find.