Take off the clutch lever and have a look at the metal pin and ball. See if they are carved in or dented or anything.
On the pin, as you use it, you will find the end which makes contact with the ball will dent in, and the side which makes contact with the lever will have carved or scratched and all.
If this is the case, then you need to replace them. If the ball is still spherical, and the pin in good condition with flat sides, then it's something else.
But in accordance to before, my guess is poor quality pin or ball so they are wearing out quickly, requiring you to constantly tighten up the clutch.
Once you have checked them, or replaced them, check the other side. Take the flower nut out, the cover, and spring. Make sure it's all in good condition. Check for any foreign objects, and put it back again.
Once you have the flower nut on and all, check the clutch cable to make sure its tight.
My guess is poor quality pin/ball, or somethings broken inside causing it to not function correctly after a while, where removing the nut helps loosen the problem or whatever it is, but as you run, if there's a piece stuck, it eventually just rides back in again and jams or whatnot.