Microsoft Dynamics CRM has a decrease in performance after installing Symantec Endpoint Protection (SEP) 12.1 or later.
There are several technologies in the SEP client that can impact the performance of Microsoft Dynamics CRM.
Microsoft has created the following best practices documentation for Microsoft Dynamics CRM.
https://blogs.msdn.microsoft.com/crminthefield/2011/01/24/anti-virus-exclusions-for-microsoft-dynamics-crm/
On the SEP client, you may also need to disable Browser Intrusion Prevention if a host exclusion does not work.