The basemap with a projection other than WGS84 is not displayed in the Basemap Gallery widget in ArcGIS Web AppBuilder but is viewable in the web map, although the initial web map of the basemap is the same projection.

Workaround

Create a custom basemap and add it into the group:

1. Open a new map in Map Viewer.
2. Add the NZ basemap.
3. Remove the default basemap.
4. Save as a web map.
5. Share the web map with the custom basemap group.
6. Update Basemap Gallery settings in Portal (Organization > Settings > Map) to use the custom basemap group.
7. Open a new map in Map Viewer Classic and choose the NZ basemap.
8. Save and create a Web AppBuilder.
9. Navigate to the Widget tab and add the Basemap Gallery widget.
10. Check the Configure the Basemap Gallery widget and the NZ basemap is displayed in the list.

Alternatively, if the owner of the item is changed from 'esri_livingatlas' to another user that does not start with 'esri_' then the basemaps work as expected.

Steps to Reproduce