Editing the thumbnail via an image file in the ArcGIS Portal Metadata Editor does not update the thumbnail in the content item.

Workaround

Edit the thumbnail, not in the Metadata Editor but in the content item.

However, updating the thumbnail in the content item saves a lower-resolution thumbnail image. See the following defects and enhancements:

• ENH-000128593: Enhance the resolution of the Thumbnail when added via Portal for ArcGIS after the layer was published
• BUG-000169739: When saving the metadata in ArcGIS Online, the thumbnail for the feature layer is replaced with a low-resolution version of the image. (This defect appears to have been resolved in ArcGIS Online, but the defect status does not yet reflect this).

Steps to Reproduce