When a webmap includes external sources that are not saved as ArcGIS Online items, the request to take maps offline fails when looking for the source ItemID.

Solução Provisória

If adding the external source as an item in ArcGIS Online, and adding it to the webmap, the data gets an ItemID from ArcGIS Online that is included in the request where the request doesn't fail.

Etapas para Reproduzir