Basemap thumbnails do not display in the Portal for ArcGIS basemap gallery

Description

After configuring Esri basemaps for offline use in ArcGIS Enterprise, thumbnails for these custom basemaps do not display in the Portal for ArcGIS Map Viewer basemap gallery.

Cause

Possible causes include:

• Incorrect configuration when setting up offline basemaps.
• Browser caching.

Solution or Workaround

Complete the steps outlined to resolve the issue.

1. Sign in to the Portal for ArcGIS Home page with an administrator account.
2. Navigate to Organization > Settings > Map > Basemap Gallery.
3. Select the group with the custom Esri basemaps from the Basemap Gallery drop-down list.
4. Navigate to the Item Details page of the web map used as the organization's custom basemap. Launch the webmap in Map Viewer, and ensure the basemap layer is referenced correctly. For more information, refer to Portal for ArcGIS: Use your own basemap . Click Save > Save.
5. Clear the browser cache.

The thumbnail displays on the Item Details page of the webmap, and in the Map Viewer basemap gallery.