I currently have two internal only maps. One is for our Sewer network and the other is for our Water network. I have secured the services so they aren't visible without signing in. I have configured the proxies. The maps have been working just fine until the day I was out sick (of course).
Now I've got tickets coming in with print issues. I can't tell if they have always existed, or are brand new, because when we developed these maps they were SUPPOSED to be temporary and replaced by a proprietary system that will be managing our fluid networks.
But basically, every aspect of the web maps works just fine. EXCEPT... Print.
We've had this issue periodically, for which this same issue happened to us yesterday. We resolved it by un-sharing, save, then re-sharing in Portal the map services that were giving us the issues. It was a simple fix, but took time to figure it out that was our issue. You may need to clear your browser's cache too.
Not sure why it works on AGO, but not internally.
A clue for our issue was that not all layers were throwing the error, just the map services that had sharing problems. Plus those same problem services were causing issues in the attribute table widget.
Do you get the error right away after clicking the print button? Also, check out what is happening in your browser's developer tools.
I guess I should add that we are using WAB Developers Edition. Not sure if that has any impact.
So that I understand you, you're able to print two secured services in AGOL with the ESRI topographic basemap?
Are you using a Utilities/Print Task located on your internal server or ESRI's default print task that's located in AGOL?
So it appears that the issue is utilizing Secured Services with Unsecured Print Services.
I'm not sure why this BECAME an issue, but the problem has been resolved.