Head-Scratcher: Sudden Oauth2 Errors on Community Connector

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We were baffled today by sudden Oauth2 errors and a forced re-authorization on a Data / Community Connector we use internally to connect to Google Business Profiles API. 

In Looker we get this debug message: 

Exception: Request failed for https://businessprofileperformance.googleapis.com returned code 401. Truncated server response: { "error": { "code": 401, "message": "Request had invalid authentication credentials. Expected OAuth 2 access token, login cookie or othe...

The connector worked flawlessly for about a year without an error--our code didn't change, was there some change on Google's end? A temporary API outage?

It's a real head-scratcher folks.