If you’re having a performance or behavioural issue with your horse, then you absolutely should look at potential physical issues first. You need to immediately consider that your horse is in pain, and that’s what’s causing them to respond the way they are.
You should try to find the source, and do everything you can to ensure they are healthy and happy in their body.
But even if the vet, and bodyworker, and farrier have all taken a look and can’t find anything wrong, it doesn’t mean your horse isn’t experiencing pain, or wasn’t and is now worried that the pain will return if they move in a certain way.
We can’t ask them why they are behaving the way they are, and it does no harm to give them the benefit of the doubt. They could still be in pain, despite every effort made to track it down. They could be fearful or confused.
Remember that behaviour is communication. They aren’t trying to ruin your day, they’re trying to tell you that something is wrong. Listen.