I'm in the middle regarding this friction stiffness thing.
If you do not consider friction in dynamics, the animated mode shapes may show Y supports slipping freely in the horizontal plane - like an air hockey table. With any sort of normal load, that will not happen. I would go back and rerun the modal analysis with artificial guides or use that friction stiffness factor. (I typically use a value of 1000.) What's nice about the friction stiffness factor is big normal loads get stiffer perpendicular restraints.
Take a look at your output to confirm your input.