Here is some more information:
We are set-up on a reverse proxy, using Portal 10.4.1 that is federated and using a SQL server. The basemap is the only outside service that we are using and has been configured per ESRI’s documentation. No other issues using Web Apps in Portal or other services.
My original error was the token error with the basemap, once that was configured correctly I started getting the subject error after about 50-75% had been downloaded.
Haven’t tried making another web map but have tried different published map services with the same results.