Horse suddenly refuses to lift back hoof/ back up?

Hi, I'm having an issue with my horse, and it's quite a recent one for him, he's never done this before.

Recently my horse lost the shoe on his front left hoof, so he's had no turnout and has only been ridden inside. Today he got his shoe back and was turned out.

When I was picking his feet all went well with the first three, till I got to the back left [not the front, the back.] and he simply REFUSED to lift it! I tried EVERYTHING, putting every only of my weight into him, pinching the leg, scolding him loudly, smacking him, begging him nicely, patience etc. If I did budge the hoof he would pick it up for a tenth of a second and quickly slam it back down. I tried it all. It took me all of 15 minutes before my trainer noticed I was having some problems, and intervened. She was more successful with the smacking him and leaning into him than me, but still. It was very very unusual for him. I checked the hoof when he lifted it and nothing seemed wrong with it, so me and her chalked it up to him being naughty.

Another thing I have noticed is when I go to back him up [because he is hard to turn I usually back him up to a clear part of the aisle to give him full turning space] he is being very difficult abut it. I will push him on the chest, pull back on the lead and everything I usually do but I he stand firm! When he did back up, he would take one full step with his right hind, and then a very short tentative step with his right. Again, a very new thing.

I checked the back right for swelling or heat, and there is none apparent. I took him into the ring and lunged him before I mounted to see from the ground if he looked off, he didn't. When I mounted him same story, no obvious lameness.

What do you guys think could cause these sudden behaviours? And how can I correct them?

I'm sure someone else will have more insight but my horse has had a multitude of foot problems and has done this on and off. To me, it sounds like he is a little sore but if nothing else is going on or showing signs of pain, heat or swelling it's probably nothing. See how he is tomorrow and the next day -- my guy would always get better after a day :)

I have this wacky theory that because he has been off balanced, due to a lack of a front left shoe, and now he's balanced again, that he's feeling a bit awkward with his back left. But again, what a bizarre idea for me to concoct.

Since all of these issues just suddenly appeared after the issue with the lost shoe, I am going to be the first one to say that he is likely in pain. Even if it isn't in one of his feet, pain in his back, shoulder, hip, etc. Could make picking up his foot and backing up uncomfortable or even painful for him. Do you know how he lost the shoe? Did he maybe over-reach and yank it off? Did he run around, buck, and play when you turned him back out? He could have pulled a muscle somewhere or maybe slipped his back or something out of place. If this was an ongoing battle, then I would say it was likely a behavioral thing but since it just started happening out of the blue, there must be a real reason for it other than him just feeling like being a butt.

He lost it out in the pasture being silly, it's odd though cause he hasn't had a shoe since thurdsday [the farrier came just today] and he hasn't acted this way.