Loopback flags were indicated as a possible issue. After deactivation, tests still failed.
One of the following references was the real culprit:
There were references to one of these that I was not using and part of a cleanup.
I believe that it is:
Description from NuGet:
Integrate with Azure DevOps Server 2019 and Azure DevOps Services from desktop-based, ASP.NET, and other Windows applications. Provides access to shared platform services such as account, profile, identity, security, and more via public REST APIs.