Well, if he is just coming off an injury and pins his ears when you ask him to move in the round pen, it could be that he is not as healed as you think.
you say he is ok with "other ground work", but I don't think it's necessarily the type of ground work but rather the level of pressure that is put on him. So, when he is not under much pressure he accepts without sass, but when the pressure is up'd, such as having him run around the round pen, then he is ready ato push back at you. his pinned ears is pushing back at you.
I would very first be sure that there is no pain issue making him want to resist moving faster than a walk. Then, get someone who is very confident to help you break him loose. He is stuck and will need someone who can project more confidence than he can intimidate with his pinned ears and posturing.
You, having had some bad experiences with him, will prbably be unable to do this, and if you arent' 100% certain you WILL do it, then don't , because if you push harder to break him out, and he ups the ante and you give in, then you have simply taught him how strong he can get without having to give to the human.
Usually, when a horse comes to a new property and starts out doing great, was great at the first purchase exam/try out , and then goes downhill from there, it's the rider's fault. (sorry) She isn't keeping his manners sharp in all the small ways, so the horse starts expanding those small ways and getting more and more pushy until it cannot be ignored.
After you get some help with this, find out in what ways you need to be consistently expecting, no, requiring obedience, and then DO them.
Selling the horse is also a possibility. Not every horse is suited to every rider and all, but if you think it might have something to do with your level of leadership, then it may be an issue again, with the next horse. So, consider this an opportunity to expand in that area with a good teacher.