Proprioception has changed with the pulling of the shoes. Even a small amount of "yield" through the hoof that wasn't there with the shoes - also perhaps different breakover - has changed the whole way the energy returns through the leg. Forelegs are particularly sensitive to this.
I was thinking about this off and on all day.
I decided if he either trotted or cantered to me today when I called him that I would work in the ring with him. If he walked, I would just walk him on the hills in hand. He trotted so we did some ring work on the lunge but on the track.
We always start walk left and I just decided I would just start left even though that is the concerning direction. And he goes left all the way down the first long side on about 15 feet of line. Then he stops and tried to turn 4 times on the second long side. Then it gets progressively sticker.
Then we go right and he doesn't have a single care. He trotted just off me starting to run. We went around the track three times and he is definitely sound now. He is also sound going left. So he is sound-sound.
Now seeing he started out fine to the left at first and then it got sticky, I thought of Bats79's comment I reposted above. He is sound so why the reluctance. Then I started telling him WALK WALK SLOW WALK WALK WHOA WALK WALK etc.. He suddenly becomes relaxed and walks about 15 feet out on the lunge. He will walk relaxed left as long as I am reinforcing that I want walk or slow or even halt (which he blows thru now for some reason). The reason he was willing to walk on the track at first is because we always walk at first. He knew I would not ask for an upward. He becomes concerned if I stop telling him WALK or apply any pressure even with my body position to do more.
The answer is he is concerned about me asking him to trot or canter going left despite the fact that he is sound. If he thinks I will not ask for an upward he will walk left on at least 15 feet of line relaxed.
This solves the walking left part. I still have to wait a bit more to ask for trot although he did do a bit of trot the other day which is how I know he is still sound in that direction.
At the vet recheck, I will ask him about going back in shoes. I think the heel looks pretty good and he is sound now. If the heel underruns again I will have to have a different plan.
Thank you Bats79. I owe you a big favor for planting that idea.