I have carried my beloved regular the last month and did quite a bit of dirty outdoor work including sprinklers, retaining wall, trimming trees, planting, and general maintenance. I noticed periodically the knife would develop lock stick but I found a very effective solution.
The lock stick seemed to occur when grit would get on the lockface either from my dirty pocket or after using it for some dirty work. One evening I cleaned the lock face with this little rubber dental brush. Just a few of swipes across the lock face when the knife is closed removed the fine grit, I could see it on the brush, and the lock stick immediately and completely disappeared!
I repeated this trick a few times over the last month with the same result every time. Complete elimination of any lock stick.
It is interesting that this knife seems sensitive to dirt because in my memory my 21 has never developed any lock stick. However, since the solution only takes me a couple of seconds it’s pretty darn satisfying.