@tttadam I think I find the issue. If I shut the pycom down by pluging it out (like the 99,9% of the cases) the sensor wont work. But if I reboot it after I pluged-in then it does work. So my "solution"/workaround is that I check in the boot.py if the checksum is false, if it is, then I do a machine.reset() . Any more elegant solution is welcomed :D