On this scant bit of information, I'm offering the following:
1. He's still in pain - it may be residual from the knotted muscle or there was another spot that you missed. This needs more testing.
2. His tack does not fit him properly and is causing pain. You could post photos here if you'd like to get some commentary from our tack specialists on the forum.
3. He is sound and the tack fits him but he has excessively high energy levels. He then needs his diet scaled back - lots of hay but not so much (if any) concentrates; he needs to be turned out in a large field/pasture 24/7 if possible.
4. He is a horse that only does best with the skilled, experienced rider. If he's got multiple people riding him, if he's getting too much ring work, if he's not getting enough riding - these are all factors that can and do affect his response to any given situation and creates bad habits. In this case, you'll need to come up with a rehab/retraining plan to get him back on track. The best and safest way is to hook up with a good trainer. If that's not possible, then you've got to start researching, reading, studying everything you can to help you develop a safe and workable solution for both of you.
Good luck and keep us posted.