Sometimes you'll get glue jammed on the hinges. Othertimes you didn't bevel the control LE even.
Other times you didn't set the servo arm correctly. Othertimes you didn't aligned hinge slots correctly.

If you didn't use sometype of lubrcaint on the hinge line of the hinges, sometimes it'll get stiff.
Liquid travel up hill or gets absorb uphill. The fibers on CA hinges will absorb accordingly.

If you have a computerized TX. You can re program the servo's center position.
It is however suggested that you get it as close as you can to a 90/90 manually.
You can also dial out the travel movent on just oneside of the servo using a computerized TX.

It will be stronger pulling than pushing due to flex of the rods.
I think it's in a pulling position for down elevator, though.