FWIW, my horse’s stifle issue only showed up when he was trotting r/h circles. His stifle never really hung up, but he would bring that leg forward more slowly in an attempt to avoid the discomfort and sensation of the patella momentarily catching on the femur. He also tended to sometimes want to swing that hindleg out a bit as he brought it forward. Many people never even noticed it, but the consequence was that when pressed to get quicker with that hind leg going to the right, he would fall into canter. It used to be much, much worse when he was in a different program where he got little to no turn-out, was lunged for 15-20 minutes 5-6 days a week, but got very little actual riding. I moved him last year to a different place where he is getting about 5 hours of turn-out every day on a hilly pasture, is no longer being lunged at all (I think the lunging we did after his stifle procedure was the first we had done since I moved him). He is also now getting ridden 45 - 60 minutes at least 4 times a week, so he is much fitter and stronger, and the stifle issue doesn’t bother him nearly as much.
We wanted to do this procedure last year, but the vet wanted him fitter before we proceeded, so we spent this past year building the horse up. He has some really nice butt muscles now, and his topline looks SO much better, he looks like a different horse. So we went ahead with the stifle procedure to address the very slight “hesitation” he had with that one hind leg, in hopes it would make him more confident bringing that leg forward. Again, we are only 3 weeks in, but we are pleased so far.