If a sync hangs and a 'The communication object, System.ServiceModel.Channels.ServiceChannel, cannot be used for communication because it is in the Faulted state.' error is thrown within the sync logs.
This error can be triggered by a number of issues, so depending on the steps taken below the cause can be unique to the instance of the error.
If this happens on 9.3 - 9.4, see the following.
Check to see if the Ektron Windows Service is started.
If it is, ensure that the knowledge files have been backed up and cleared as detailed in the following KB article.
Confirm the total amount of disk space needed for the physical files of the site and the site's database, and compare this to the receiving environments free disk space. Our support team recommends having twice the sum of the following folders: assets, private assets, uploaded files, and uploaded images.
If the error message persists then a sync to a min database may be needed to resolve the error message. It is recommended to reach out to our support team for confirmation or further assistance.