There doesn't seem to be a problem there in the Xbox version, that I could find. I did encounter clipping issues a couple times falling through the ground when Rush Attacking uphill (fortunately with a recent save each time, though in at least one case I could run in the direction of lower ground to get back above ground).
There is a spot on the river in Broken Valley, near the entrance to the fjords, where you can swim into the cliff and try to jump a few times to fall under the water (which will then disappear), and you can run along the riverbed (jumping up to where the surface should be or moving into shallower water will get the character swimming as normal). There is a dark patch of rock you can see below the path on the cliff, and I found this out while trying to see if it was just the colouration or a shadow (ie possible cave entrance or a hidden ledge).
Welcome to the forum.
