I have noticed recently that our custom print services are no longer working from web apps that have been created by Web App Builder Developer Edition and published to the web server. If I access the web app from WAB, the print services work fine.

The error description says "Error executing tool. Export Web Map: Failed to create layer from service at" then lists each service in the map. I unfortunately just stumbled on this error and do not know when it stopped working. Does anybody have any ideas?