First of all there is several reasons why camera buttons can stick in the housing. One of them is that camera body is different from time of use, specially joystick on D800, 810 and similar Nikon cameras. Its not the same hardness on camera with 5000 shutter count and with 100 000 shutter count. I personally test this and notice this problem and differences in hardness between camera joystick due time of using . We in Subal test every housing with camera inside and adjust every button after assembly. We also have quality control with several checking in pressure chambers as well. Our cameras in company are used only for checking and they are pretty new with very low shutter count and also not many buttons movement. After adjusting and quality control we can't predict does housing will come to someone with camera with 100 000 shutter count or more and in what conditions camera bodes are.
This joystick button is very sensitive and every hardwer changing on the camera body can cause sticking, for example rubber base on the bottom of the camera, if its thiner or damaged can cause not proper alignment on the camera tray and after some buttons, specially joystick can stick.
Every issue that we found out from customers and they are not many, we try to solve, and we focus seriously on problem. Subal ND800 housing is 5 years old housing and one of the top product with not so many issues and complaining with sticking or else. I personally use it for 2 years with not any problem. But as I mention, issues with sticking can be solved with new lever inside with wider plastic on it and sticking will stop.
For frequently used cameras and soft joysticks we made additional levers inside with wider plastic that press joystick with more surface on it. If someone have this kind of problem we can replace this levers inside and sticking will stop. Also we prefer in this situations that housing be adjusted with the camera from user.
For all informations contact your local dealer or Subal directly and we will consider and solve the problem.