Windows 2012R2 Master on 7.6.1.1

Check name resolution - a DNS server responding slow can cause those type of issues.

Use the nslookup command - not ping as it may use WINS for name resolution.

A fellow Trusted Advisor recently shared the following Performance Tuning advice:

1. The paging file was set to automatic. It has been set to a fixed value 64GB (twice the physical memory) and set to use the F drive which has the most free space.
2. Increased the number of worker threads available to Windows using the following registry keys (note that the RpcXdr\Parameters\DefaultNumberofWorkerThreads needed to be created):

These recommendations (and more) can be found in:

The NetBackup Backup Planning and Performance Tuning Guide, Release 7.5 and Release 7.6  
 http://www.symantec.com/docs/DOC7449

There is also this forum post that deals with EMM tuning:
https://www-secure.symantec.com/connect/forums/simplest-questions-reasa-db-threads

Hope this helps.