Upgrading to 11.3, Completed Portal, but just says Unauthorized

[CW-GIS]

Upgraded to 11.3, no issues except a warning about language packs. When I go to our URL, I just see this:

It wont even go to the sign in page. We haven't upgraded server yet (well in process), but I never remember seeing this in past upgrades.

[ReeseFacendini]

If this is Windows, make sure the service account is set correctly to run the Portal for ArcGIS service (it may have been set to "Local System" during the upgrade), and that same account has full folder permissions to ..\ArcGIS\Portal & ..\arcgisportal.