Adam:
Thanks for the feedback. I actually had multiple problems with my setup that needed to be addressed. Unbeknownst to me another active directory account had been remoted into the server (or a lock was being held onto from this account which was resolved by rebooting the server) and this type of account blocks all internet access including to AGOL (enhanced security to prevent MalWare attacks).
I then found out that the self-signed certificates used for the base Enterprise deployment for AGS, Portal, and the DataStore are not adequate for Collaboration tasks. ESRI tech support assisted me with installing the proper domain certificates for AGS, Portal, and the DataStore using the same certificate that had already been installed and configured for the web adaptors.
The Collaboration now works for me, but there are some workflows that I would have like to have used which are just not possible (e.g. Copying web apps from AGOL to Portal - the ESRI tech support specialist did inform me that this workflow can be done in the reverse direction Portal to AGOL which would not meet my current collaboration workflow needs).