All of my problems even when I thought it was the button were center contact issues. Now to test your button to rule that out.
Calibrate the meter: Turn the dial on your meter to ohms the omega symbol on the lower left put it on the 10. With the probs not touching the needle should be to left and pointing at a sideways figure 8, infinity symbol. Touch the probs together the needle should go to the right and point at zero. if not at zero adjust the screw so the needle points to zero.
To test the button: first test it at rest, touch one lead to the screw the other to shiny spot anywhere on the aluminum plate. Meter should read zero or very close to it. lift a prob and the meter should go to the left again.
Now the tricky part that might take
three hands. While holding the probs on the silver screw and the aluminum plate. press the button in and wiggle it around. It should always read near zero, if it jumps to the left you have found a spot that is losing connection or you lifted one of the probs. I could not get mine to jump to the left.
The way the button works is: Current flows up the screw to the plate in top of the button. Current transfer to the spring from touching the screw and the plate. The spring transfers current to the aluminum plate. When you press sideways on the button the screws contacts the aluminum plate transferring the current and bypassing the spring. electricity takes the easiest path.