I am currently dealing with a similar situation! I own a 7yr old CWB, who is a big dude with a ton of scope. I always feel safe on him, if he does buck/rear/misbehave its in such slow motion he doesn’t stand a chance of getting me off. At home, he is amazing, super consistent, very good boy. When we get to shows its a different story, and like you said, every time I enter the ring I have NO idea what I am going to get. Even the warm-up ring is always consistent, its just that darn show ring! I have spent far too many trailer rides home in tears because of frustration.
After my most recent show, where we barely got around the ring, I decided I needed to finally “draw a line” and decide when enough is enough. I left the ring and told my coach “This isn’t fun anymore”, and like previously mentioned in other people’s posts - if it isn’t fun then why are we doing it?!
And so, with my coaches advice, he is going to put in some training rides one/twice a week and see where we get. He will also show him next so maybe my horse will gain some confidence out in the show ring! Then, when I show again I will drop down in height and see if it makes a difference.
In the end I truly feel my horse is a good boy! But I think he doesn’t have the greatest work ethic, and knows how to throw his body around to get out of work.
I will continue my current program and see what results! I have a soft “deadline” of a show in October, where if there isn’t any change in him then I know it will be time to part ways. But I am truly hoping he will get his butt in gear and start being more of a team mate!
I wish you the best of luck, and I hope you will keep everyone posted on how things turn out and what you decide to do 
