"Invalid Credentials" error creating new dataflow that uses On-Premise Data Gateway and SQL Server

I'm having the exact same issue- just started showing up about a week or two ago. 

Previously we had no issues.  The only thing we can figure out that changed was when we applied the October gateway update (going to try to apply the November update tomorrow.)  Credentials are known valid, and multiple users have the same issue. We are able to create a new dataflow ONLY if we add the root folder of the gateway to the dataflow, save it, refresh it, (sometimes manually map the crednetials in the datflow settings) then go in an add the correct entities, deleting the dummy root folder entity. Then we're good.

Again we didn't change any credentials, users, security groups, or other settings intentionally and had a working setup in production previously.

We really have no idea where even to look to figure out what could have changed.