I had similar issues with Kontroniks in the past and never solved them.
But I also had recently similar issues with Tribunus and with HW recently. In both cases telemetry was not working when motor was running, or when motor was running and there was a higher load on it. In both cases problem was gone, when I grounded the FBL/RX to heli frame. I'm not sure if it's a correct solution, but it worked for me, made many flights with it - works fine, no crashes.
Also, if you want to make your own cables, maybe this will help you. In Polish, but you should be able to google from there. This is what I've bought in the past to make them. It is possible to do them with pliers without the crimping tool, it's just more work. But I don't remember which AWG version I used.
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