New layers added to a service via the REST endpoint do not display automatically on the item details page.

Workaround

After adding the new layer to the map through the REST Endpoint, copy the map URL and add it as a new item in ArcGIS Online.

1. Navigate to Content > My content.
2. Click New item.
3. Click Feature layer > Provide an ArcGIS Server layer URL> Next
4. Paste the URL and click Next.

The new layer appears on the item details page of the map.

Steps to Reproduce