Anyone experiencing that the thumbnails for the default basemap gallery do not display (Portal for ArcGIS 10.3 newly installed)? There is a screen shot below where you can see that some display while others do not. This occurs when viewing in multiple different browsers and the Collector app. I placed a ticket with Esri and they had not seen it before and are working on it. I wondered if others had experienced it and know a solution? I tried to manually assign a thumbnail to the basemap details page but because it is Esri content assigning a thumbnail is not available as an option. Any ideas where these thumbnails reside on the server, if I knew the location I would test out placing the thumbnail there assuming I got the naming convention correctly.