Problems with the switching behavior of the reed contact already arise with the Shelly Door/Window and now also with the successor Shelly Door/Window 2.
Unfortunately, the manufacturer's instructions contains nothing about this.
Well, I'm working with such contacts for a long time. All of my DW have been working reliably and flawlessly since installation.
There are actually only 2 points that you have to pay attention to:
1st:
The distance between the evaluation unit and the magnet can be 2-5 mm. Direct contact of the magnet with the unit is absolutely of no advantage and can even have a negative effect.
2nd:
1 small arrow is printed on the side of the evaluation. This marks the middle of the reed contact. Also place the magnet in the middle. It will look like that:
I wish you success.