While you were detail cleaning one thing you would have come across is a reddish-brown oily substance all over the internal parts of the pistol. This is a shipping lubricant/preservative placed on the pistol and its components at the factory. This substance tends to attract residue and become more viscous over time causing reset malfunctions like you experienced with your new pistol. The disconnector lever depends on the upward tension of the trigger return plunger and spring to reset on the sear. This tension is nominally only 4 to 6 ounces of upward pressure. It doesn't take much resistance to prevent the disconnector lever from raising up and resetting the sear. Any powder residue on the top of the trigger, or down in between the disconnector lever and the frame, will create enough resistance to prevent proper functioning of these components. By thoroughly cleaning out behind the lever you have reduced the drag on the lever and likely solved the problem.
Also, the top of the trigger is an area where powder residue tends to congregate after use. If this problem returns you may want to consider opening up the plunger hole on the top of the trigger slightly. I usually use a #10 (0.1935") twist drill bit for this operation, take care not to deepen the plunger hole, just open up the diameter slightly to reduce drag on the trigger return plunger from blow-by powder residue. Opening up this hole dimension allows for less friction on the return plunger after high usage. This slight modification gives you more range time between the need for deep cleanings. The plunger hole is sized originally at 0.1910" and the #10 bit is the just next size diameter larger.
Hope this helps.
R,
Bullseye