We were playing in a world with Experimental Gameplay turned on and we were traveling on horses through the overworld. We regularly run into invisible walls that we cant run through, and have to relog to make it go away. When this happens, the player appears to be standing in one place when other players look at them, and doing the glitchy shaking that animals always do. I thought it was caused by the Experimental Gameplay, but it also happens in our world that does not have that turned on.