I have this issue a lot, I am pursuing high performance riding but currently am schooling 2nd-3rd level. I instead shoot for more short term goals but have my real big goal there. This year my goal is to get some regional Training Level Rider Test Achievement awards, debut my first USDF recognized show, and really get into showing First Level, as well as showing two other horses that are much more of a struggle for me at Training Level and Intro. Sometimes we plateau in riding, I did in the fall, I felt stuck. But those times you feel stuck are valuable, you hone skills and search for ways to progress. It sucks, it absolutely does, you feel helpless. "How can I perfectly time this half-halt?" "How do I use my body to half-halt?" "Why is my horse blowing through my aids?" are things I used to ask myself, and eventually I started to learn to use my body after reading up on half halts and doing barn work! Barn work also helps you strengthen parts of the body you didn't know you had! Riding is a mental thing, it tests you a lot. Its discouraging to feel stuck, but I promise you, these times where you feel stuck, you are learning. Talk to your trainer, and if you feel that they have no idea what to do, I would begin to trainer shop. Luckily my trainer understands and is open to new ideas and may put me on a more "push button" horse to help me figure out if well, I actually CAN push the buttons, or she may put me on a more challenging horse to see if the challenges arise on that horse (They do! They become more obvious to myself), or she may get new exercises that take it back to basics.
Another way that motivates me is watching professionals, I live by the USET and got to see the Young Riders and Grand Prix Freestyle at the Festival of Champs and that really pushed me to work so I had the possibility of showing at that level when I'm in my twenties!
I had this problem when I was emotionally attached to a coach that wasn't challenging me. I wanted to switch but I liked her so much as a friend and person that I felt awful. For about 2 years I didn't learn barely anything new! And as soon as my mom finally made me let go and get a new one I was back to progressing . Find someone who is going to challenge and push you outside your comfort zone
I would definitely suggest a new trainer or coach, or you can do some exercises or try new things.
But it will probably be your trainer that's the problem so definitely think about how she/ he teaches you and think about where your going with her/him.
And focuse on getting to the point where you do start processing faster or something happens because there's no point in waiting for something to happen, you have to want that goal , you have to maybe change a few things like your horse or your coach or your stable or your attitude.You have to get to that. Life can sometimes be hard but guess what it's hard for everyone, sometimes harder or easier for others but it does get better trust me!Hope that little lecture helps
My mentality is always "Even if I improve 1% a day, after 100 days it means I progressed 100%"
Consider a new trainer and try new activities
I am new to Horse a lot but I would try something new for a bit and then come back or try something different in his/her schedule.
First of all, never forget that progression isn't a constant thing! It is totally normal to have periods when you progress less than before.
My advice would be to settle some objectives and work to reach them. Be indulgent to yourself, you can't always succeed everything.
If you have a trainer, feel free to speak with him, I'm sure he'll uderstand and will help pass through this period.
You can also try to work a bit differently than you currently do. Maybe try another discipline?
Good luck with that, I'm sure that if you persist with working you will soon start progressing again!