My apologies for the delay in getting back, I was away on holidays for a month.... 
Is the issue resolved ?
I looked at the snapdrive logs:
I see some errors in SD logs:
10/19-12:36:15.615 PID:23240 TID:30192 filer.cpp@6164 The 'license-list-info' ZAPI is being called.
10/19-12:36:36.662 PID:23240 TID:30192 filer.cpp@6169 Failed to get the list of licenses on the storage system 'Netappdr'. Error code: 13011. Error description: RPC Error - The RPC server is unavailable.
Possibly b'cos of this error in the SnapDrive, it falsely report following error in the SnapManager logs:
Error code : The storage system volume is no longer a SnapMirror destination.
SnapManager just orders SnapDrive to perform acitivity and for some reason if SD fails to act on certain task, it results in SnapManager report misleading errors such as that.
Cause: Possibly an issue with useraccount trying to ZAPI to remote fier. Please note, manual snapmirror update usually works in such scenarios.
Please provide us with this info:
1) What is the service account used for SnapDrive activity?
# example format - 'DOMAIN\netappsvc'
2) Please send me the output of this command from DR filer.
Netappdr>useradmin user list
3) Also, if you could forward the 'messages' log from the Netappdr filer, it might have captured 'access denied or missing capability' sort of errors.
Log location on Netappdr: /etc/log/messages*
Netappdr>rdfile /etc/log/messages