Transmitter not connecting

I have a FlySky PPM receiver and transmitter set that I am trying to initialize my PixHawk board with.

Previously, this connection has worked fine and I was able to calibrate the Radio in QGroundControl and receive signals to the board.

Over the span of the last few days, (without changing any of the equipment on the board), I have begun to receive a message stating “0 Radio Channels detected” even though I didn’t have this issue before.

The Receiver’s connection to the board seems to be fine as the receiver is getting power and is connecting with the transmitter.

What are common causes and/or solutions for problems like this?

Much Appreciated!