In Web AppBuilder for ArcGIS, if the Basemap Gallery widget's basemap consists of an image service and vector tiled layer basemap, the image service overlaps the map services, which are added at the service level.

Workaround

Use either one of the following:

• Use Esri cached basemap in the custom basemap, such as <a href="https://services.arcgisonline.com/ArcGIS/rest/services/World_Topo_Map/MapServer" target="_blank">https://services.arcgisonline.com/ArcGIS/rest/services/World_Topo_Map/MapServer</a>, and use the service level services in the webmap that are used to create Web AppBuilder.
• Use Esri vector tile basemap in the custom basemap, such as <a href="https://basemaps.arcgis.com/v1/arcgis/rest/services/World_Basemap/VectorTileServer" target="_blank">https://basemaps.arcgis.com/v1/arcgis/rest/services/World_Basemap/VectorTileServer</a>, and use the layer level services in the webmap that are used to create Web AppBuilder.

Steps to Reproduce