Simple pushbutton board acts like its shorted but does't measure shorted
In a clean design even a 200k switch open resistance should not cause malfunction. Do you use external or uC internal pull-ups? In case of internal pull-ups, what voltage will you get if you calculate with 200k switch open resistance and lowest supply voltage? Is this voltage still be in logic-high range?

There is no such thing as a perfect switch/button. I usually calculate with 100 Ohm closed and 100k open.