From ArcGIS Web AppBuilder in ArcGIS Online, if a map displays categorical data greater than five categories, the legend does not show up upon exporting the map to any file type from the Print widget.
Last Published: November 26, 2015ArcGIS Online
Bug ID Number
November 18, 2015
September 22, 2022
After review by the development team, it has been determined that this issue is related to a known limitation with the software that lies outside of Esri's control. The issue's Additional Information section may contain further explanation.
This is a known limitation. By default, the Legend element on the layout tries to fit as many items as it can. When it finds that all legend patches from one layer cannot be fit, the entire layer gets dropped. In this case, most likely the Legend element is running out of space when more than five categories are used.
Create a print screen of the ArcGIS Web AppBuilder application while the legend is in the field of view.