Haven't stayed here before, but came across this in a search:
AIRPORT SHUTTLE SERVICE ALERT: Effective May 17, 2021, shuttle service will become pay-per-ride and hours will be 4:00 am to 1:00 am.
(unable to post links yet, but it's on the main IHG page for the property)
Appears to be $10/person round-trip (that is from the home page on their "independent" SFOCP site) . First time running into a US IHG property with "airport" in the name that charges for an airport shuttle. I've seen airport properties that have suspended shuttles over the last year, and at least onee airport property that is opting not to offer a shuttle, though.