Strange radio failsafe before flight using Crossfire / CRSF

Hi guys, I’m investigating an odd failsafe that occured before flight, with an F405-WING using CRSF with Nano Diversity RX and a QX7 (unmodded). AP is 4.1.0-dev (still a version from October).

The plane was approximately 10m away from the transmitter when a radio/throttle failsafe occured for which I can find no reason when I look at the log:

  • CH1 never went down to FS value

  • CH12 which is LQ (Crossfire’s RSSI) never dropped either (although this might be misleading as AP keeps showing full RSSI when it drops directly from full to zero, for example, if transmitter is switched off)

Side note: I didn’t have my FPV goggles on yet when the FS occured, so first I didn’t notice the plane was still in RTL when I tried to launch it afterwards (and the FS was cleared) - hence the failed attempts to throttle up seen in the log.

It looks to me as if the transmitter didn’t trigger the FS, so it must be something else?

Additionally, passthrough telemetry via CRSF wasn’t working (“no telemetry”) - although it did perfectly when I last flew the plane months ago and I had not changed any settings.

Even though the short test flight went ok afterwards, I definitely want to get to the bottom of this, as this was my first time using AP after almost 5 months of winter break, and it’s not a good start having this confusing occurence.

Also I had some failsafes last autumn testing a 10" ArduCopter (same radio/RX setup) that I never was able to fully explain either - although in that case, interference from an onboard cam might have been the cause.

Thanks for any hints.