Tachometer for my bike

Hello,

this weekend I got my reed switch from Sigma and connected it to my pico (GND and B3). As proposed, I set the pin to input_pullup and wrote a basic watch function:

setWatch(function(e) {
  pincounter++;
  console.log(pincounter+"\n");
  },
  B3,
  {repeat: 'true', edge:'rising', debounce:10}
);

Now I get some strange behaviours with different options:
edge: 'rising' no debouncing
Most of the time two events when moving magnet to sensor and one when moving away.

edge: 'rising', debounce: 10
One event when moving magnet to sensor and one when moving away. The same for debounce 100 and 1000.

edge: 'falling', no debounce
Three events when moving magnet to sensor and no event when moving away.

edge: 'falling', debounce: 10
No events at all.

Not exactly what I expected. Am I right that it seems that the reed switch only closes very short but not keep closed while the magnet is next to the sensor?