I've just upgraded our enterprise from 10.5 to 10.6.1.
I found the following thread that suggest the service directory may be corrupt and have checked our configuration (refer to below).
Our IT department have removed internet access for the ArcGIS Server. So I'm assuming that the Server needs internet access to render the previews via arcgis.com? Do I need to allow internet access and add a rule allow traffic to ESRI only *arcgis.com?
Is there an option to use this offline?