Hi everyone, this is my first post. I am an junior hunter rider (3 foot children's hunters) and I just got a new hunter 2 months ago after a 6 month break from riding. He is a lovely horse, amazing jump and movement. But we have one problem here: When I am flatting only, and I pick up the canter on the left lead he will swap on the long sides of the arena after a couple steps. When I first got him it wasn't bad but its been getting worse and worse. It is not a soundness or soreness issue as he just got injections and a full vet check. I have tried keeping him intensely bent to the inside with both of my hands to the outside which worked for a few times then he swapped. He gives me warning when he is going to swap by hopping a bit and putting his head up and when I que him to canter forward or pull either of my reins he swaps. I have also tried holding firmly my outside rein which kinda works but he still swaps eventually. When I canter him on the long side, he tries to come off the wall and I pull him back or push him to the wall with my inside leg then he swaps. He is extremely sensitive and I believe the issue is my own error and lack of balance because I had two of my friends ride him and he didn't swap. I have tried changing each body part individually as well as not doing anything and letting him canter loosely and it feels like nothing is working and my trainer is at a loss because he has no idea what I am doing to make him swap either. I am at a loss, any advice will help. When he does swap I usually just trot then pick up the canter again only for him to swap a few strides later. I believe I am doing something to que him to swap but I have no idea what I am doing and my trainer can't figure it out either.