Hey Michael,
That's the issue. So, to resolve this issue,
1. Unfederate the ArcGIS Server & Portal.
2. Uninstall the web adaptor from the machine. Then, install the web adaptor two times - one named "arcgis" or "server" and "portal".
3. Then register "server" with ArcGIS Server & "portal" to register with Portal for ArcGIS.
4. Re-federate Portal & ArcGIS Server.
5. Setup the hosting server.
Please let me know if you can open Insights & create a new workbook after this.
Thanks,
Aravind