Hello,
I completely agree with Samuel's Comments.
When uninstalling the SEP client (Group Update Provider), take a Backup of the SharedUpdate Folder.
SharedUpdates Folder could be found -
SEP 11 - C:\Program Files\Symantec\Symantec Endpoint Protection\SharedUpdates
SEP 12.1 -
(32 bit machines) C:\Program Files\Symantec\Symantec Endpoint Protection\12.1.x.x.x\Bin\SharedUpdates.
(64 bit machines) C:\Program Files(x86)\Symantec\Symantec Endpoint Protection\12.1.x.x.x\Bin64\SharedUpdates
When the SEP Client is reinstalled, create the SharedUpdate folder (in the above location) and paste the complete content which was Backup before.
The SEP client would work flawlessly without any issues (once assigned as GUP on SEPM).
By performing the steps above, the SEP client would only download the required definition updates which are lacking (instead of entire updates) on the SEP clients, saving good amount of bandwidth.