Update:
The hump on this CO-2 was slight, but enough to get a bit of low string buzz if I played around the 12th fret or higher. I finally got the time and desire to take it apart at the same time. I took pictures, that I may post later. In short, it seemed like something was allowing the neck to be tightened up in a way that had the fretboard extension to need to rise slightly as it set on the top. I didn't see anything obvious. We're only talking a mm or two. There are four Allen screws that hold the neck in place. One near the end of the fretboard, two side by side much closer to the neck block, and one going through the block into the heal of the neck. Getting the Allen wrench inserted into the screws, over and over as I tried things, did take patience. Eventually, by the proper order of tightening and not torquing any one screw down until all were snug, improved things. I think I would have to be looking for it to now see the hump. I can play up the fretboard now. I think a mm or two taller saddle would allow me to play louder , that high up and not buzz. No buzzing with a capo on the 7th fret, etc. If it stays solid. after some serious, I'll be a happy camper.