Hey,
I hit this issue today while learning new MI-8. Yesterday I`ve configured Mode1,Mode2, and Mode3 switches as pilot seat changer. These were detected by DCS as JOY_BTN_34, 35 & 36.This morning it stopped working, so I got here. Your suggestion worked only for single mode change, as if I tried to configure other mode changes as "no button" option it was blocked by logitech editor as already used option.
So I found another way to do this. When I opened logitech profile file (.pr0) following section appeared for Mode1 configured as "no button".
We can clearly see that Mode2 & Mode3 have some nested selectionset & buttoncombo objects. I just removed them using text editor and functionality works as it should for all 3 buttons:
It seems like it gets broken each time when I open the file in Logitech editor and naviate to mode editor.
Hope it will help someone!