Thanks for the tag! The communication with the Hubitat Cloud Relay is fine. Anybody who already has their location and devices authorized can continue to use them.
It appears to be limited to the OAuth servers.
That links to this thread on the SharpTools community:
Hubitat OAuth Connection Issues - #2 by josh - SharpTools.io (web) - SharpTools Community
It describes what's going on and a workaround for users who already have their hub authorized and just want to update their device selections. And it points to the following Hubitat Community thread:
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I would note that this is impacting other integrations that use OAuth to connect to Hubitat including Google Home and IFTTT as well. It seems to be an intermittent thing, so as @bobbyD noted, sometimes just waiting a few minutes and trying again solves it.