While riding on a horse, (chestnut in color and wearing a saddle with iron horse armor, or no armor at all in my case) whenever you ride up an elevation change upwards the horse will likely get "stuck" preventing you from moving forward anymore.

When this happens you appear to move up the block but the horse doesn't, resulting in you looking like you're floating above the horse. This isn't 100% replicate-able, but happens almost all the time. To "fix" this, you can just move backwards before jumping above the block. However, jumping up the block is tedious when you're moving anywhere that isn't relatively flat and nearly impossible when climbing anything resembling a hill.

I've linked a photo of how you appear above the horse while this is happening.