Since he had these issues, I really took my time and treated him as an unbroken horse. I restarted him. He is fantastic!
The problem began to really show up again when I introduced him to riding outside. I was told he had been camping. LOL funny. Honestly I thought he was more than ready and I never expected a huge issue.
However, his response to stress is still to do a pop up. Not a full rear but plenty serious enough if it were to escalate. What is upsetting about it is that even though I am experienced, very light handed and ride him forward he still manages to convey the threat and ignore my aids even on a relaxed rein! I have been working him on a direct rein in small circles, gradually expanding my territory. It is working but admittedly it is not a good feeling. I do not trust him. He swishes his tail too which makes me think it may have some aggression thrown into the fear.
Opinions and recommendations from seriously experienced riders/trainers would be appreciated. I am probably on the right track and I am pretty sure he has done this to someone else. I am confident but he is far superior strength wise. He popped in front and when that did not work he went right to crow hop. All I could do is just keep his feet moving. I was thinking to ground drive him outdoors before I try again. Sigh. He is so nice and smooth, generally quiet until he gets stressed. I would love to keep and show this horse but I don't want to get hurt. I wish I had been told about this.