PROBLEM
Images can be added to ArcGIS Online or Portal for ArcGIS content, and they can be used as the custom image symbology for points in a web map. In some cases, the symbology referencing the hosted image is not displayed in Map Viewer.
The hosted image in ArcGIS Online or Portal for ArcGIS is not shared publicly. The image used as the custom image symbology must be shared to Everyone (public) so it can be accessed and utilized across multiple web maps and web applications with different sharing settings.
To resolve the issue, change the sharing setting of the hosted image to Everyone (public) in ArcGIS Online or Portal for ArcGIS. Refer to ArcGIS Online: Share items with everyone for steps to do so.
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