Does the M3 cap screw have an anti-vibration “patch”? (That looks like a blue or white colour blob of thin paint on the threads) Many screws in the Form2 do.
Its worth applying a decent soldering iron (at least 50w or the iron from a temp controlled solder station at 280c) Leave it on the screw head for 20 seconds and then try the Allen key again. Heat softens the “patch” - too much heat will damage the screw so be careful.
This is what “patches” are like
