The micro switches under the metal buttons are cheap and will stop being reliable after about a year of regular gigging use.
If you are handy with electronics, open it up and clean out all of your switches whenever this starts happening. No need to re-solder a new microswitch. The procedure is very simple, in essence: locate the micro switches, and apply liquid DeoxIT to them, and press them a few times. I like liquid (not spray) DeoxIT, because it's only one drop, nothing gets sprayed in the process, you don't need to be careful where you spray, etc. The switches to me became as smooth as butter after the cleaning.
watch a video on how it's done. https://youtu.be/WONiwe0vjH0 Helix is built like your typical Chinese gadget (Kemper floor is no different): looks solid from the outside, but inside is all microscopic PCB stuff with cheap components. In particular, the little button plungers are not held by anything, if you flip the unit upside-down they will all fall and you will not find them.
you need a big table with a towel for this job -- can't do it on your lap.
I use Tupperware / bowls / shot glasses to store all the parts, like screws/bolts/nuts. Sort all your screws by height, etc.
Take a picture of what's inside before you start taking things apart -- that way will know how it used to be. A tablet is very useful for these.
When I cleaned micro switches on the Helix LT, I did not have to take apart any ribbons, remove any glue, etc.