Maps and Apps Gallery 10.1.1 does not display its gallery if a gallery item does not have an icon, and the new ArcGIS Online content items are not created with any icon.
The new content types do not have a default thumbnail. The Gallery was updated to handle this new ArcGIS Online behavior, and the change has been made available in version 10.2.
Note: As of April 2018, the Maps and Apps Gallery app template is in the Mature Phase of the ArcGIS Online Product Lifecycle. For more information regarding support of this app template, refer to the Maps and Apps Gallery requirements page.
To correct this issue, do either or both of the following steps.