If you can tighten it, and it loosens over time there are two likely possibilities.

1- the crown race or a head tube cup isn't seated fully and is settling. This is common on newly fitted headsets, but eventually cures itself since at some point the crown or cups will bottom out.

2- the stem is slipping up the steerer. I've heard of this but never seen it happen. The vast majority of riding forces are on the lower stack so only the reaction force acts to move the stem up. But it's possible, and the traction compound you're using should solve it.

If you can never get it truly tight, look for s sloppy fit. Usually it'll be at the lower head tube cup where the tube has become bellmouthed over time. It could also be the crown race, or one of the other cups. To check, drop the fork and check everything. I've also seen the steel races get loose within the cups on certain headsets, and on integrated headsets the bearings not seating properly.