No Reverse
With some ESC's i note that if you are quick off the mark after switching on Tx, RX the ESC can still be in set up mode , so i adopted the switch on Tx Switch on Rx and count to ten policy years ago seems to have worked over many years. Found useful more so 2.4 sets if lots of sets in use as they seem to take a few seconds to find a frequency , and having a smart phone go into search mode very near, 1 metre is not helpful, depends on make. Brushless speed controller , start in middle pos for throttle stick dos motor start and run if so throttle to full reverse and return to midpint i have a couple that have that issue as all our rc is aeroplane based on throttle stick being idle at bottom , full at top marine speed controller or car has fwds and back reciever gets confuesed is it a boat, is it a plane hope this helps going forward.