I`m having bad time with my DOUTs too. It worked OK before with 1 or 2 modules but now, when I have 4.. same thing as urban_soul. I also have 100uF and 100nF capacitors even i never use it before for 1 module. Soldering seams OK. I tested each module with DOUT testing app and everything worked OK. I noticed that length of interconnection affect this issue before, so I keep the wires very short. I`m too pretty much sure it is some kind of ground problem or such as touching the PCBs with fingers stabilize it. DINs seams much more unforgiving in longer chains than AINs, even I would expect other way. What is left for me to try is to use bigger, 470uF instead of 100uF capacitor at input and see will it help.