If it dies when you put it in 1st gear it is most likely the kickstand neutral safety switch having debris and needing to be cleaned---when you move the side stand lever up it should activate it. There is also a bypass under the left side scoop where there is a relay you can remove. I wouldn't fill the reservoir up as the fluid expands when hot-try lowering the level and cable tie the lever to the handlebars leaving overnight to see if you can get all the air to rise to the top. There is also a neutral safety switch plugged into the clutch lever.
Yes, a good suggestion. Some WD-40 or CRC 5-56 squirted on the shaft should allow it to slide well, and to perform properly. Squirt, and manually operate the shaft until the spring mechanism actuates the shaft properly when you activate the kickstand. With the kickstand down bike in neutral and running, when you put it in gear, the sidestand switch kills the bike to keep you from trying to ride-away with it down.
If is due to clutch drag then I would expect the bike to jump forward before it stalls.
