Hey @cbrauweiler,
the fact that you can send properly shows that the problem might rather be related to your receiver hardware. What have you got there? Iām asking because some receivers are really bad. I used to have a bad one myself. (bad means that you have to put your signal within a range of a few centimeters to be actually able to receive something)
See: https://forum.pimatic.org/topic/3052/help-homeduino-not-working-anymore-solved/116