Many times I've seen rotary encoders with worn out or dirty contacts cause the adjustment to only go in one direction no matter what way it was turned. It's never been the electronics itself.
With tact switches, a lot of times they are all arranged to shunt an ADC line to 0V via a resistor, with a different value per button. You can see one resistor per switch, usually located adjacent to it. When the switches wear out, their contact resistance rises and adds to the shunt resistance. This then mimics other switches or puts them out of a valid switch reading range.