The reason why many people don’t improve is because they do not communicate effectively with their horse. You’re aids are of extreme importance at all times! Pay attention to the details. My main tip is to film yourself and then have an expert or instructor give you their opinion. I also recommend researching because that might help you improve. Hope I helped!
most of the time, this is because the rider and the horse are always doing the same thing. Same discipline, same horse, same work, same instructor, etc. Try something real different, take risks, don't be afraid of making mistakes or going outside of your comfort zone. It can be tough and you can even feel lost for a while but you will learn something which will help you to improve eventually.
There's a multitude of reasons why you could have possibly stopped improving:
-You or your horse could have reached your limit. It could be that you on a different horse, or your horse with a different rider would go further. It could be that one, or both of you have reached the top of where you are going to go.
-You've reached the end of your own knowledge and need to further it before either of you can improve.
-Your instructor has gone as far as they can go, and you may need a different instructor.
-You're going through a bad spot. It happens to the best of us.
-One or both of you need a break.
I've ordered them from (what I think, and you can completely disagree) least likely to most likely, so I would start with taking a break for a week or two for both you and your horse. If that doesn't work, persevere for another while. If there's still no sign of improvement, I'd change instructor and see if that makes a difference. If not, I'd start retraining and up-skilling. If none of that works, I would look into loaning your horse while you rode another horse. It could be that this is as far as you/your horse will go in a particular discipline. I would try the rest first, but it might be no harm to start considering other disciplines.