I am familiar with this issue having had a few of them myself.
Introducing them to company in the ring is critical. Try and ship to a place or two that has less traffic than the schooling ring at the show. Or pick a schooling ring and time at the show that is less busy. Try and avoid crowded schooling rings. Be very alert and careful to avoid horses coming straight at your horse. Stay away from those situations as much as possible. Practice oncoming traffic avoidance.
The horses I have had with this issue have gotten better over time with this management. The problem subsided but still remained. Fresh horses are apt to do this more than tired horses, so think about that as well.
If there is another quieter place to warm up for the show ring during the show, find it.
At home you should be able to find times to ride where there are less horses until your horse gets more comfortable with this. They are legitimately afraid so punishment does not work, and only complicates the fear factor.
