a few month ago I had to face some failing of switch 4, sometimes it worked, sometimes not.
I contacted Kempersupport and they told me how to check button-functionality.
I did it and everything worked fine: I pressed the button a hundred times with my finger and the machine counted exactly 100 switch operations. I did this more than only one time.
However, as soon as I returned to "normal rehearsal business" the button returned to it's unreliability, too.
The result of this now is, that I strongly hesitate to play a gig with this machine - on the other hand there is no gig in sight - you know why
The Kempersupport told me, I must wait untill the button fails in a way, that the check mode prooves the failing - what my technical mind has to accept .
The other day I read of someone who had opened his Stage doing some cleaning of buttoncontacts which solved his problem...
for now I decided to live with the situation watching what will happen...