Basemap is not available. Displaying the default basemap instead

Error Message

In ArcGIS Online, opening a web map returns the following error:

Error:   
Basemap is not available. Displaying the default basemap instead.

Cause

The following are possible causes for this issue.

• Certain web browsers and browser settings can prevent web sites with mixed content from drawing completely.
• The basemap may be temporarily offline.
• ArcGIS Online is referencing an incorrect tile layer URL. This can occur if the tile layer is deleted before being updated or if the name of the tile layer is changed.
• Incorrect security settings. The organizations security settings use HTTPS, however the service URL for the basemap is referencing a HTTP URL.

In addition, there are known issues in ArcGIS Online and Portal for ArcGIS caused by BUG-000099434, which is triggered when a web map is opened that references an unavailable basemap.

Solution or Workaround

Try one of the following workarounds to solve this issue.

• Temporarily disable any extensions installed in the browser that may interfere with the ability to load the basemap, such as Privacy Badger.
• Configure the ArcGIS Online security settings to allow HTTPS connections. 

Note:
Organizations can apply a domain filter to determine the domains that are allowed and restricted within the organization. Domain Requirements for ArcGIS Online provides a list of URLs which must be added into the organization's allowed list for ArcGIS Online to have full functionality.

• Only use browsers supported by ArcGIS Online.
• Ensure that Cross-Origin Resource Sharing (CORS) is enabled in the web browser. For more information, see Cross-Origin Requests in Internet Explorer, Firefox, Safari and Chrome.
• Use the Beta Web Map Viewer to manually repair the service links or select a new, working basemap.
• Use the ArcGIS Online Assistant to manually repair the service links of the updated tile layer. Replace the tile layer's service URL with the newly updated service URL.

Note:
The ArcGIS Online Assistant can also be used to determine if mixed content is used by inspecting the web maps JSON. For more information, see ArcGIS Online: Troubleshoot.