Although your position is "nice", you are riding very defensively and it is most evident in your shoulders, arms and wrists. I would be tempted to put you on the lunge without reins on an older horse to get your upper body more relaxed and your seat swinging through instead of locking in a driving position (as it is in many of the pictures). Some exercises on the lunge that would be good for this is reaching down to your right foot with your left hand and your left foot with your right hand, doing windmills, airplane arms, etc and lots of half seat to get your muscles to relax.
Otherwise, you need to sit more to the front of your saddle in order to encourage your seat to swing and allow the horse to really carry you forward. Your shoulders really need to come back to open your chest and you should not have chicken wings for arms - elbows in! Physically place your elbows onto your hips - it will also help your shoulder posture. Beyond that you always need to be relaxing your forearms and wrists. Unkink your wrists, put your thumbs ontop and shorten your reins so that you aren't tempted to put back or tighten the elbows and restrict the horse infront. You need to be very light and quick in the contact - keep it alive and feeling - have an interesting conversation with his mouth.
Training wise - I feel like your restrictions upfront are having some consequences. He is moving downhill, BTV, heavy in the hands and far too slow. As you are able to lighten your own contact, work to really get him pushing forward from his hind legs to actually cover some ground. His poll needs to be the highest point and your conversation is all about not letting him get hung up on the bit - you are bouncing energy back to the hindlegs with the contact.
In the canter I'm betting you feel like he is running and you want him to go slower. Resist the urge to pull him up infront and sit up and ride at the speed he wants to go. As he is more balanced and learns to step under himself he will naturally come back to you. Grab mane if you have to and keep the contact soft and feeling without pulling back.
Good luck! And like I say, there are no glaring errors - just details, and the devil is in the details.