Training issue come mainly from one source - people. Therefore as the person who has to solve the issue you have to sort of reverse engineer the problem. Get to a stage just before the horse shows signs of the issue and look at what the next step is that causes the issue and stop there. I am not saying to let the horse get away with whatever it is doing, just observe the steps taken to reach that point.
The next step you should take is to do something else completely different. If your horse is anticipating the issue to arise, but you do something else, the interest is taken away in whatever it is used to doing (i.e. the "issue") and now doing something completely different. Do this a few times and then go back to the issue.
If, for example, your horse takes a step away from you when mounting, make all the movements up until the point of mounting, and then perhaps lead him on and around in a big circle. This will break his anticipation of mounting/stepping away and distract him. You would need to do this a few times, to "throw him off". Then come back to the mounting. If he has begun to anticipate you leading him on, instead of mounting, he should stand. Pat him, and tell him how good he is. If, however, he still steps away, another, reverse action can be taken, for example, mounting from his opposite side.
Horses are two sided animals. You cannot do one thing to one side without doing it to the other. However, very few people think to mount from the other side. They just are so not used to doing it themselves, that it is almost as though you have landed from Mars. But - and I cannot emphasise this enough - you must teach your horse from both sides. So obviously you need to learn from both sides as well. If this is awkward for you, practice on a barrel or something for a while till it is easier. You probably have to retrain your muscles.
We only mount from the near side because it is "traditional"; soldiers kept their swords on their right, so the mounted from the left (near). But we are not soldiers and do not have swords (at least I hope you don't). So there is no real reason why you cannot mount from the other side.
This sort of reverse engineering an issue will keep things calm and not spooky and you and your horse can work fine together. Just put a little imagination into it. You will also find that your horse appreciates a break from "routine" and will probably repond more brightly as well.