There is a bug with the speed visual upgrade on the Kagouti Fabricant mount. Foot geometry seems to stretch into the ground when moving, and also the side of the seat rotates with the leg becoming misaligned.
Here are several pics to illustrate:
The issue goes away when speed upgrade is hidden in gameplay options, so it doesn't seem to be a problem with the base model. Other mounts I have don't display this bug with the speed upgrade shown and running repair in game launcher doesn't fix it.
This is on the PC with maxed out video settings.