I may have found a possible cause: Last night and today while watching the MCU load I noticed, that either the MX-20 or the GR-12 telemetry kills my WiFi: No WiFi devices visible at the router anymore. No other transmitter had done this before.
This brought me to the idea that either the transmitter or the receiver (which is only a few centimeter away from the BT module) interfered the BT connection which ended up in corrupted data when trying to edit parameters. I reflashed the fw today, reloaded all parameters and flew 30 minutes without any issues.
What I would like to know is: When I switch off the Graupner radio, does the GR-12 receiver still send data or not?