Hi,
Also check is there any following fix id relates to your issue. If yes test with SEP 12.1 RU2 version.
Reference: New fixes and enhancements in Symantec Endpoint Protection 12.1 Release Update 2
http://www.symantec.com/docs/TECH199676
Applications are slow to launch over the network
Fix ID: 2756476
Symptom: Applications are slow to launch over the network after Symantec Endpoint Protection client is installed. Disabling the SymTDI driver resolves the issue.
Solution: Updated the SymTDI driver to improve performance of large networked files.
ThinApp portable applications are slow to start from network share
Fix ID: 2645151
Symptom: Applications that are packaged as VMware ThinApp portable applications are slow to launch when the application is launched via a network share.
Solution: Modified the Auto-Protect driver to honor exonerated network files when the network scan on execute option is enabled.
Performance of App-V applications is slow
Fix ID: 2825796
Symptom: Applications using Microsoft Application Virtualization (App-V) are slower to launch and slower to execute.
Solution: Modified a driver to allow the scanner to store cached data in memory for App-V virtualized applications.
File operations too slow with Symantec Endpoint Protection client and SOXBOX agent
Fix ID: 2662063
Symptom: Symantec Endpoint Protection client and SOXBOX agent installed together cause file operations to run too slowly.
Solution: SymEFA no longer enables an NTFS change journal for the SOXBOX agent's hidden NTFS volume.
Excessive non-paged memory used by Symantec Endpoint Protection client
Fix ID: 2733231
Symptom: The Symnets.sys driver (pool tag SND1) slowly consumes a large amount of non-paged pool memory, eventually leading to a system crash.
Solution: Updated the SymTDI driver to resolve a non-paged pool memory leak.