I also can't really ride either. Happens in both single and multiplayer.
23:23, July 30, 2019 (UTC)Same happens to me. Both single as well as multiplayer
See https://lotrminecraftmod.fandom.com/wiki/User_blog:Glflegolas/A_fix_for_laggy_horses
You probably downloaded the mod via Firefox as a .zip instead of a jar (Firefox does this sometimes).