I experience this frequently in towns, and lately in Thunderhead Peaks (once during an Adventure, and fell off a bridge as a result... ouch). It usually lasts 2 to 5 seconds, then resolves, but sometimes lasts up to 10 seconds, or until I get impatient and just dismount. My marker on the minimap still moves as I use WASD or my mouse, but my character is rendered with her legs in the ground from the knees down, with my camera standing perfectly still behind her. This happens on both my desktop computer (Win 10, RX 580) and my laptop (Ubuntu using Wine, Quadro M1200). I'll see about taking a video capture tomorrow.