My M9 just got this problem after many years of use. After try many solution include factory reset, reinstall firmware, downgrade firmware etc. nothing solve this.
So....my last resort, because my warranty ran out, I took off enclosure and clean the knob with " contact cleaner spray. "
BOOM! My problem solved! every knob function as it should be again, knob can go to max and engaged tap tempo mode.
**beware when apply cleaning spray, you shouldn't spray on the knob's pole, it will lose knob's friction that make it feel like cheap audio device! and also hard to fine-tune adjustment.
