Quick update on my build. I managed to fix two out of three dcp405 modules. One had soldering issue on shunt sensing opamp, another one had output enable resistor badly soldered (see the pic, although it was the other side of resistor, I wasn't able to take a good picture of the problem). In many cases visual inspection didn't help much, I had to probe with a dmm to detect failures. Soldering is actually quite bad, even though at first glance it doesn't appear so. I suspect they have problem with soldering paste, the alloy feels brittle or not completely melted or something. The board also produced cracking sounds when I dried the board with hotair (the temperature was well below 100C, I could keep my hand). I hope that weren't solder joints cracking...
My last dcp405 is a bit more difficult. I resoldered a few ICs with hot air, many joints resoldered with my leaded solder just in case, also found one disconnected capacitor (see the pic). The CC mode still misbehaves: it outputs 21uA when set to zero on low current range, and oscillating ~0.2mA on hight current range. Sometimes it outputs 22mA on that range when set to zero amps. I'll continue my investigation.
Meanwhile I found that common ground coupling didn't work. It was T2N7002AK,LM from toshiba which failed open between source and drain). My very-very first dead mosfet! I replaced it, and replacement died the same way... ESD problem? EMF from relay? I checked zenner across relay, it appeared to be working. I replaced the mosfet with 2N7002-7-F from diodes inc., and it worked. Weird, isn’t it?