Just checked out the multiplier days on the GSR website. This footnote appears after the description of the multipliers: "Individual players may be disqualified from point multipliers or may be given a reduced multiplier for any reason, including suspicion of advantage play, based on the decision of casino management."
Grand Sierra disclaimer
My husband and i were told at the Players Club that we were ineligible for the multipliers because we were “skilled players.” If you are excluded, there is a notation on your account on the kiosk-there will be an “X” next to your tier level.