Kakute F7 frsky telemetry issue

I have a Taranis x9d+ (original), X4R receiver and Kakute F7 AIO as a flight controller.
I have set SERIAL6_PROTOCOL to 10 and SERIAL6_OPTIONS to 7. Pass-through telemetry used to work fine (with occasional hiccups but that’s ok). I had to use 4.0.0-dev for a while as at one time only there there was a logging support, so I sorta got used to it.
After near-crash and rebuild (nothing to do with ardupilot) I flashed an updated 4.0.0 and did a quick test - it was all fine and because it was quick I might have missed an issue with telemetry. I set my quad aside for a month or 2.
Yesterday I wanted to do some flying and noticed that telemetry starts ok but after about 20 seconds it just freezes. The quad still responds to inputs and flyable, just no telemetry. Turning radio off for a few minutes helps a bit (for another 20 seconds), same with FC.
I have tried re-flashing radio, FC with both stable and dev version of copter 4, changed sd cards on both radio and FC, switched logging off on FC completely, checked that no other ports have PROTOCOL set to 10. I have re-created my model on TX also. No luck so far. Any ideas?

Some telemetry systems have specific SR* parameters, and having them wrong can cause similar issues.
Not sure about X4R, though.

Those are stream rates I think. I’m not sure if they affect frsky pass-through telemetry.