A map service with a width and height tile information other than the default (256x256) fails with the basemap gallery and Basemap Toggle widget.
Bug ID Number
November 17, 2015
June 2, 2021
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.
The thumbnail image is displayed using the basemap's thumbnailUrl. This is not displayed in the sample application.