Endnote X9 "Sync" error

Since this ‘emergency maintenance issue’, I am having problems syncing my attachments. I get an error message "  An error occured while trying to replace the attachment. Please try again". This first occured when Endnote was down a week ago, but I have not been able to sync attachments since getting this notice. 

Are you able to assist me short of asking me to download the entire library again please? 

Thanks!

Library details

Sync Details
Sync was last run: Tuesday, November 13, 2018 at 12:53:26 PM +1100
Sync Status: There are changes that need to be sent.
Error Code: Server.ReferenceStore.internalError
Error Message: An error occurred while trying to replace the attachment. Please try again.

Local Sync Library
Library Name: My EndNote Library
References: 5821
Groups: 73
Group Sets: 7
Attachments: 5883

Online Sync Library
Username: 
Serial Number: 3091850007 (Premium until January 10, 2019)
References: 5821
Groups: 73
Group Sets: 7
Attachments: 5851 (4.26 GB)

Sync Limits
Number of References: 1000000 (994179 can still be added)
Number of Groups: 5000 (4927 can still be added)
Number of Group Sets: 5000 (4993 can still be added)
Attachment Storage: Unlimited