Boot the device into test mode by holding Func and powering on, select trig one to go into test mode.
Take a guitar pick, a butter knife if it’s thin, or a bit of dental floss if your dexterous and pop the key cap off by leveraging the bottom of the button. Don’t do it from the side, due to the way the keycap clicks into place. Press your lips to the key, blow into the key, depress it multiple times, then blow into it again. Take a small cotton bud and run around the edge of the button to pick up any crud. A quick hoover of the exposed button may help, but with a disclaimer that there may be a risk of static discharge, however small.
Repeat until the key no longer jitters when depressed. Only reason I said test mode is it’s generally easier to see if it’s still jittering. This might take a few attempts. I’ve done this to my yes, midi and 5 key and am no longer having any issues with it, they were awful before. This might not always work as the key may have a worse underlying issue like a bad solder joint or the key being loose on the PCB, but definitely worth trying. On a side note, I’ve had to do this a few times over the course of a week to properly dislodge whatever was stopping the circuit from closing properly, trig 5 still plays up but is getting better each time. Yes works perfectly now.
On a side note, you can click the DATA/LVL knob in menus to avoid pressing [Yes], if this fix doesn’t work for you. This tends to be more reliable than a jittery [Yes] button. Doesn’t help for previewing triggers though!