It could be a million different things.
Assuming it is not a configuration problem:
Having trouble with increment/decrement (modes?) could be debris in the side tube, but that would be isolated to that one tube.
If other mouthpiece holes are not responding (no lights or lights not following the sip/puff) at the same time, it could be power supply voltage related.
If the supply voltage drops, the pressure sensors will act like there is a sip. If the supply voltage increases, they will act like there is a puff.
The most common reason for a supply voltage drop is a poor USB connection, with a worn out cable, or worn out socket on the back of the quadstick.
It can also be the quadstick is sharing power with some other USB device that is pulling a lot of power, like a USB disk drive.
Check your connections, try a different cable, try a powered USB hub, check the mouthpiece for dirt. I get quadsticks in for repair all the time that have nearly completely clogged mouthpieces. I have no idea how they continued to work, they are so completely blocked