I have made a custom print service for my webapp. All of the layers in this webapp are hosted on AGOL and are shared to specific access groups - but they are not public (this is by design and the layers display perfectly to all group members in the app). The custom print service is hosted on my organization's arcserver.
This arcserver has a webadaptor URL that is configured via a reverse proxy.
I am using the WAB print widget.
Using the print widget with the web adapted print service URL returns "Error try again[...]execute status 0" if any secured layers are displayed in the app when the print service is called. It WILL process if all of these secured layers are turned off.