Check your wiring for loose connections, the following issue was solved after I re-seated the servo connector back into the Rx:

https://www.youtube.com/watch?v=frkmoMhQ5AQ

The following issue was solved after fixed the HV servo harness:
https://www.youtube.com/watch?v=LneubAZ5oX0&t=35s

Solution here:
https://www.rcgroups.com/forums/show...0#post40061288

Also note that it can be anything from an incompatible servo with your ESC and myriad of other gremlins if the glitch buster doesn't solve your issue after checking for loose connections