OWA - gives following error
"Your session has timed out. To protect your account from unauthorized access, Outlook Web Access automatically closes its connection to your mailbox after a period of inactivity. Please re-enter your user name and password. "
Confirm the Authentication on the IIS Virtual directories as below
Default Web Site -> Anonymous Authentication Only.
OWA -> Basic Authentication Only.
Try and disable Form Based Authentication (Enable Basic authentication from EMC) and then test OWA and confirm if your session still gets timed out.
Try Disabling Thrid party AV