The problem could be corrosion on the slider pot, a problem with signal processing in the firmware, or the gimbal calibration needs to be run. (not the calibration you just did, that one has nothing to do with the issue.) It could also be a hardware mismatch if you swapped the left button board into the other controller.
Let's do some checks.
1.) If you swapped the left button board into the other controller, skip to the end and start by doing a
Channel Calibration.
2.) If you did not swap the button board over or if you have already done a channel calibration, then
open "Hardware Monitor" (system settings/OK/Hardware Monitor). Move the gimbal slider up and down. "K2" indicator should move smoothly up and down. This checks the Hardware.
3.) If the hardware looks good, check the S
ignal Processing. Go back to the main controller screen and do a quick double tap on the battery "Volts" icon. This will bring up a box with a bunch of scales on it. Move the pitch(tilt) slider top to bottom again. The indicator for CH07 should move smoothly top to bottom. It may indicate a couple of percent off on either top/bottom or both, but no real worries if it's pretty close to 100% in each direction.
3.) If both Hardware and signal processing look good, you need to do an actual
Channel Calibration. Either of these videos will help. The absolute key to success is that BOTH sliders (camera tilt on left, Rabbit/Turtle on left) on the sides of the controller
must be in the center position prior to changing screens.
ST16 Calibration Video Links