You could try grid work, especially bounces, that way he has to pay attention to what he's doing and not just charge blindly. You could also put a rail a stride away from the back side of the jump (similar to a grid) so he has to lift his feet up over that after. Again about getting his focus
Also when you lung make him back up by yanking hard. I have the same issue with the mare I work with she won’t stand still while I tighten her girth and so I make her work by marking her turn in tight circles around me but before I make her back up and move her feet @aabby
do you already use a double bridle
Do pole work and many transitions, especially downward (canter to walk) so your horse is listening to want you want. Practice jumping into a line, halting, then trotting out of the line. It will take time but I promise it will help
he’s good on teeth and back! So I’ll try that👍🏻
What I would do is try a double bridle and makes your reins tight but not to tight to where it’s yanking on his mouth. Also what I would do is do small circles before you try jumping again and also try free lunging and lunging him over jumps.
Check his teeth, his saddle and his back.
If all is ok
Then trot at cross poles with 2,5 to 2,7m poles before and after the cross poles.
Don't jump at a canter until he does this nicely
Try coming into a jump from a closer distance and turn a few strides after the jump it helped me 😉