Contacted Hyatt support about another matter, at the end of our conversation she asked if there was anything else. So I said yes there is--the web site; she submitted a report. This is the follow-up email I received today:
"I did receive the following response from our IT team: Hello. This is a known issue that our app development team is investigating. This is affecting many users, at the time clearing cache/cookies is the workaround."
Wonder how long it takes to investigate, so they can get on with fixing it.