Troubleshooting Esri Basemaps (not responding) in VSW

Hello, 

I'm looking for some pointers on where to start troubleshooting the functionality of Basemaps in VSW. When adding Esri Basemaps I'm they are being added to the basemap widget but not drawing in the application. I don't think it's an issue with competing projections as the data is all in web mercator. I have tested the same basemaps in a Portal map viewer with no issue… any thoughts on where to start debugging this issue?

Cheers,

Chris