I had a similar and heartbreaking experience with a very talented warmblood that I broke in and jumped up to a high competetive level. He suddenly started stopping after being exceptionally brave. I made the mistake of blaming my own riding, and not realising that if a brave horse suddenly starts stopping it is usually a physical problem. In his case it was his back that was out - apparently very common in jumpers due to the stress placed on their backs by the landing. I would try to eliminate all physical causes. Get a chiropractor to check him, as often there is no other symptom than refusals.

It took me two years to work out the problem and treat the horse correctly.