Consider app.config remapping of assembly with no app.config mapping

I solved this by targeting a higher .Net Framework version. Switched from 4.7 to 4.7.2 and the warnings went away. The warnings started after I switched from EF6 to EF.Core

I began getting the error when I upgraded the Microsoft Identity packages (via NuGet). Some of the version numbers were not updated in the <runtime> node of the web.config file. I found this fix by following Leo Liu-MSFT's instructions (above).

How can I determine where to fix this reference without adding a binding to the app.config?

You can try to change the "MSBuild project build output verbosity" to "Detailed" or above to check the detail error log. To do this by Tools -> Options...->Projects and Solutions->Build and Run. Set the MSBuild project build output verbosity level to Detailed or above. Build the project and checkout the error log in the output window. The ResolveAssemblyReferences task, which is the task from which MSB3247 originates, should help you debug this particular issue.

Then go to the project with the older version, removed the reference, then added the correct reference.

The real problem is that the References in the .csproj file are not updated when doing a nuget update, hence the warning to override these in the app.config. If you update the .csproj, all warnings go away.