I have couple of layers in web map e.g. Parks, Museums etc. I set legend symbol of Parks and Museums as PNG image in web map.
My ArcGIS Enterprise version is 10.5.1
I created my custom print layout and published on ArcGIS server as per documented here
I changed the Utility services URL in Portal for ArcGIS and getting all my custom layout listed in drop-down.
I created app using Web App builder developer edition and adding print widget.
Now, When I print using print Widget Web App builder, Point layer features (Parks, Museums), the features on map and legends symbol (PNG image as legend symbol) drops during the printing in all the formats (PDF, PNG, JPG etc..).
If I changed Point layer( Parks, Museums) legend symbols to Portal in built symbol e.g. Pin mark symbol, its printing and visible on map as well as in legend all the formats (PDF, PNG JPG etc..).