It is very common for horses to become a bit "side sour" as we call it, meaning they are a bit of a handful and antsy one direction. The best way to break this I have found is working one exercise going that direction first, in the middle and last in a work out and doing exercises like 20m circles, lunging and those types. By repeating the direction and using the same exercises it helps them work through that problem and remember. It acts almost like a reminder for them.
Best of luck!!