CRSF causing motors to spin in dshot modes when armed

Aircraft has been flying fine with 2 types of Frsky RX including 868mhz types. I was using dshot600. I have just changed to CRSF nano. Motors jitter when armed, strong enough to be dangerous or damage props. It seems independent of RX/antenna position or TX/RC power settings. Tried all Dshot speeds 150-1200. Tried different refresh speeds. Tried moving servo wires away. (its a large aircraft so they are far away anyway).
It works perfectly in oneshot and oneshot125. Unfortunately I really want DBshot telemetry (as was previously working fine).
Arduplane on Matek H743. All latest firmware.

I may try another blheli32 if I can find one.

Any ideas?