I have a couple of Portal environments set up with a federated ArcGIS Server instance and I'm coming across the following logged error for each of them:

The service is shared with our Portal organization and not publicly. After digging a little bit deeper into the logs, I noticed that the first time a user tries to establish a connection to the services the request comes across as anonymous and ultimately reports back the error above:

Users access a web application that is hosted on a web tier machine, which is the bottom http refer link. Oddly enough users are still able to load the services with no problem as long as they are a named user. However, when I look in the ArcGIS Server logs it is flooded with "severe" level logs. Has anyone observed this issue before? The post ArcGIS Portal/Server Exception setting 'ownership' role. makes it sound like this isn't critical, but I'd like to elimate this issue from our logs. Our portal setup is as follows:
- Web adaptor/web app hosted on the same standalone box; leveraging IWA
- Portal on a standalone box
- ArcGIS Server on a standalone box
Thanks!