Indriks tilt left and right according to the bumpy terrain. It's very noticeable when riding at any speed. This does not happen with any other mount I own - only with Indriks.
(I do not use the 'foot inverse kinematics' option, because it makes horses' hooves bend forward and look like they're tip-toeing in an unnatural way.)
Pic of my character being in the same exact spot, but with Stonelore Elk vs Dawnwood Indrik