Portal for ArcGIS: Request made to publish item as new service but the item <ItemId> already exists

Error Message

Attempts to share feature layers as copies in a distributed collaboration between Portal for ArcGIS and ArcGIS Online fail with the following error message returned:

Error:
Request made to publish item as new service but the item <ItemId> already exists. Unable to publish item. Remove the existing item and sync collaboration workspace.

Cause

The distributed collaboration workspace is out of sync. This may be due to the following reasons:

• Schema changes to layers or views are not applied when the workspace is synced.
• When multiple layers are referencing a dataset.

Solution or Workaround

1. Unshare the item from the collaboration workspace group in ArcGIS Online. Refer to ArcGIS Online: Remove content for instructions.
2. Sync the collaboration workspace from the guest participant using ArcGIS Enterprise. Refer to Portal for ArcGIS: Synchronize a collaboration workspace on demand for instructions.
3. Reshare the item with the collaboration workspace group in ArcGIS Online. Refer to ArcGIS Online: Share items with a group for instructions.
4. Repeat step 2 to sync the workspace again.

Note:
If the issue persists, consider deleting the workspace and creating a new collaboration workspace.