Sacroillialc? suspensory? help very unusual lameness!!

So my 5 year old Connemara Pony was at a show a few weeks ago. He arrived the monday and did a few bronco impressions the rest of the week he was a little sticky but by his class the thursday he couldnt canter properly as he couldnt seem to get his hind legs under him. Got the chiro out and his pelvis was out 3 inhes to the right i think. He fixed him and all seemed to be well but we have now realised that he still cant canter on the left rein only. The left hind still seems to be blocked as he wont pull it under him so he keeps changing behind. Hes sound in walk trot and canter on the lunge and sound when ridden in walk trot and right canter when ridden its just left canter thats the prob. HAd the vet out and he doesnt know where the problem is so put him on high dose but for 5 days to see if that would know a spasm out. However theres no real change on the bute (maybe very slightly but not a good enough change to constider it effective). Theres no sign of heat or swelling anywhere, he remains sounf upon flexion. It seems to be to do with weight bearing but at this point im at a loss with what to do. Going to try get the chiro out again to see if he sees anything. Ideally id get a full body scan but finacially thats not an option and if i get nerve block we are going in blind as to where it is so could be very costly… im thinking its the sacroilliac as he twisted when he was juping around that day. Has anyone had anything similar? Vet thinks it might be mechanical seein as the bute didnt really help

Could it be EPM? How does he do with the tail pull and other neuro tests?

My horse rotated her pelvis due to a kick to her hamstring (it seemed insignificant at the time but was actually pretty serious). Due to the amount of time it took to diagnose her injury her pelvis still doesn’t want to stay in place but is no longer so far out of place that she can’t hold a right lead canter.

My mare’s pelvis rotates left side forward and down right side up and back, meaning that she is stuck in a left-hand turn. This makes it so that, going to the right, she tends to bend left and used to pick up the left lead going right.

She is not particularly painful, just crooked.