I reached out to the Hyatt Concierge on Twitter on January 9th, asking about the Apple Wallet functionality having gone missing from the app as detailed in my post above. I just got the following from Hyatt's Consumer Affairs team with an update that I will share below:

The recent update to the app, which added the room key function with Apple Wallet, temporarily removed the option to add stay/reservation passes to Apple Wallet unless the hotel is set up to offer the Apple Wallet room key. The app team is investigating the best way to reincorporate this function; however, we do not currently have an ETA to restore this.

So... they removed a useful function that applied to every one of their hotels to make way for a new feature that currently works at only six hotels in the United States.

Honestly, I'm speechless - this is the kind of crap I'd expect from Marriott.

khabah