I’m not an expert, but I did go through a similar time with one of my horses. You may be over-thinking it. First, my guy went through what we fondly call his “rodeo year” for no apparent reason when he was between 3 and 4. He was an idiot. Sorry, but that’s the truth. I can say that because I owned his mother, I was in the stall when he was born, and he was an idiot then, too. At 3, he discovered he could buck, and he tested his new talent at odd moments when least expected.
We got through that without much damage to life and limb (other than his, as he managed to throw himself to the ground bucking in the pasture on muddy dirt), and all was well until I had a “moment” where my winter boot velcro strap caught on a fence insulator. We were just walking along, already done with our work, and there I was with my leg pulled around till my boot touched his butt. I couldn’t get it undone fast enough (horses walk faster than it appears), and he got spooked and gave out three good bucks till I came off on my head. Smashed my helmet to bits! After that it was kind of catch-as-catch-can with the random bucking again.
I hate to admit it, but the solution that time was just plain anger on my part. He got me off, but I landed mostly on my feet (rare!) and popped back up and just yelled at him and smacked him in the chest with my crop. Just once. I didn’t beat him, much as I might have felt like it. That was the last time he bucked with me on him. He’s old now, and he could care less about moving his body to that extent. We have a fine time together.
So you could be caught between novelty and habit as I was. Don’t be too wary on the trail. Looking at every rock and twig makes you tense up and he feels that. Try to relax, even if it means only hacking out for a few minutes at a time. There are no rules that aren’t meant to be broken. Carry a belt bag with treats and a clicker. That also helped with some of my guys’ issues. I spent days walking my spooky mare out on the trail on foot, father each time, and each time giving her praise and a treat for not freaking out and dragging me along. We worked up to walking out a mile, then riding back. She wound up being so solid I used her to pony new horses out on the trail, and she did 5 miles all alone in a rain storm to rescue another rider whose horse refused to get on the trailer.
Just know it will eventually be okay. 😉
Good luck to you!
Horses In the Yard