#15926
Benjamin Bube
Participant

I found the mistake. One of the wires from the modem was too close to said sensitive module. As a result, the power cables of the modem each developed interference when sending. Placing the power cables from the other module a little further removed the problem.
I got the idea when afterward even the I2C bus said goodbye to the modem or its voltage peaks.

Many thanks for the fast reply!