QGroundcontrol hung on radio setup

I’m trying to configure my Pixhawk 2.4.8 via QGroundcontrol for bench testing. I’ve updated the firmware, connected the power adapter, PPM encoder between my Spektrum compatible Orange receiver, ESC and motor, one servo, and various other peripherals.
The receiver binds to my Tx, ESC, motor, and servos all work properly when connected directly to the receiver. When I interpose the PPM encoder and Pixhawk, the ESC/motor gives the appropriate beep sequence to indicate the ESC is receiving a signal.
When I try to set up my radio, it hangs after throttle calibration. Specifically, the display indicates movement of the throttle stick to top and bottom, but doesn’t allow advancement to the other main flight controls, even after waiting several minutes.
I’ve repeated the process several times, but the “Next” button remains greyed out, even after reloading the firmware.