I'm stuck during the training phases of this quest, I'm sat on Roach for the horsemanship training but cannot move, I can Axii roach, and double tapping shift does the giddyup animation/soundbite but I cant move, reloading my save does nothing to fix this.

Yes, happened to me and others. Return to a previous save and pick the choice NOT to do the training. Go straight to the tourney.

You don't need the practice by this time, anyway...