Sorry to dig up an old thread, but:
Recently I tried to book rooms using the Costco SET. It generated an error message at checkout.
The Hyatt Concierge on Twitter told me that the Costco rate can now only be booked on the Costco Travel Website.
Also that this rate is not considered an eligible rate and will not earn points/stay credits (but on property Globalist benefits would be provided).
Has anyone else noticed this? Are there any workarounds to book on hyatt.com?