Can you post a side view, as solar shots are kind useless with pads and shoes.
Did you take that digital, pulse at the time he was sore-ie, time past his dump of NSC, so he can have a transient slight laminitic incident, at the time that blood sugar gets an insulin repsonse that affects the hooves, for that short period?
Slight laminitis, can leave no trace, as the stress caused at that time of high Gi (glycemic Index), is not enough to cause the lamini to fail, so once that sugar rush is gone, which causes the high insulin response, which affects the hooves, dissipates, the horse will be 'normal'
So, just to be clear, you checked his digital pulse when he was sore?
Far as beet pulp, it is a required taste
Feeding Remission to a horse that is not IR, makes no sense. Any horse can be pushed over the level where he can transport a given amount of blood glucose into the cells, and why founder can occur in a horse that is not IR and gets into that feed bin
Far as thin soles, it has been proven enough times that horses don't have thin soles because of some poor genetics. They are man made, either through slow distal decent or thinning the soles while trimming
Slow distal descent has the entire foot sink lower in the hoof capsule, with that hoof capsule becoming longer, while the sole becomes flatter and thinner
Whether or not, slight low grade laminitis and distal descent is going on with your horse, it is still worth reading the info on distal descent and how it relates to sole thickness Distal Descent
And, the articled on sole thickness Horses Sole