Guild Wars 2

It seems as though when I am running, and attempt to mount, the mount does not appear, and my character is instead shown halfway into the ground. In addition to this, the camera gets stuck where my character was, leaving me seeing my character glide through the ground and into the distance, with the camera stuck where I activated the mount button. This is resolved by demounting, which fixes the camera on my character in their new position. This issue then persists for several minutes afterward, then allows me to use my mount regularly.

This occasionally happens for me as well, exactly as you describe, but only lasts for about a second or two before everything displays correctly.