kleag:
@MarkT : when the button is not pressed, the voltage between the input pin and the ground is 0V. When it is pressed, it is +5V. Seems normal...
If you didn't already, try measuring on the MKR1000 board [at pin8], and not at the breadboard [i.e. perhaps the wire is open - or is not making contact in the header -- as in smutz on the contacts].