No, it is not the set screw. If I tighten the set screw even more, then the rod doesn't slide down even in the open position.

One of my flicklock pro on my BD trail pro shock can be pull out of the pole in the open position. I checked the other 3. If it is in the open position, even with the set screw all the way out, it cannot be removed. However, this one can. The issue it causes is that it's loose on the pole, allowing rotation and sliding, so it is not in the right position to close down.

Does anyone know how a flicklock pro gets fitted onto a pole in the first place? and not be easily removed? If I were to replace this part, what is the installation procedure?

Thanks!