This response is probably a bit late but here's a check list:
- Is RX bound to the controller and have a solid green light?
- In Betaflight are the Rx settings set to SBUS and Frsky?
- Try moving the controller several feet from the RX/drone when testing. My Frsky RX always have signal breakup when they are close together...

Hope you have it figured out and if so, please let us know the solution. Cheers!