I solved it!
It turned out the Xbox controller was causing a conflict. I unplugged it and have full control of the flaps and can now adjust the heading bug in 1 degree increments again.
It’s never caused a problem before, and I don’t know what happened to cause the problem now, but I can live without the Xbox controller as I rarely used the drone camera anyway.
I’m just happy I can fly again!
Thank you for your help 