CRK specifically warns against the use of locking compounds on the 21.
I use the hell out of my small 21, in and out my pocket easily 30+ times a day, it works in grease, oil, water, coolant, salt water, gasoline, acetone, kitty litter, diatomaceous earth, you name it.... it gets washed out with a spray of carburetor cleaner typically, and Ive yet to have the pivot loosen.
Im sure if you contacted CRK theyd supply you with the torque spec for the pivot bolt so you could torque it if you have the tools. Otherwise just going tight with the supplied allen key should be all you need. tight to me is starting to just show a bit of flex in the allen key.
If none of that works Id make sure its assembled properly, and if it is...send it to CRK to have it sorted.
If you dont want to do any of that, and REALLY want to use loctite, I would NOT apply it to the threads, just place a small drop on the bottom of the bolts flange where it contacts the frame.Put it together and let it cure before use.