After Installing El Capitan I Will be Logged Out Frequently

• MacPro late 2009 with 3 monitors. OSX 10.11.1
• Will run great on 1 monitor without screen/system freeze or logouts. At times it is an instant logout, other times, the primary monitor freezes, or is filled with weird graphics. NVIDIA GeForce GT 120 512 MB
• Began with 12 G Ram and upgraded to 24 after having problems with El Capitan. Suspected OS memory leak.
• Then did full erase and OS install, but before restoring my data, created new user and used Safari to test. On each monitor, a Safari tab streaming news videos. Ran for hours, but when I started using the system, it had video problems and locked up or logged out. Don't remember which.
• Then restored all my backup data and settings.
• Activity Monitor shows full 24 G installed, but the Memory Used and Cached Files never go above 12 G
• TechTools 8, all test pass. Memory, video, temperature, fans etc.
• Apple Care 2nd level tried to no avail.
• System performed flawlessly until El Capitan install
• System now is totally unreliable. I installed 10.11.2 yesterday and am hopeful that fixed it for me as it has many others. I'll update.
• It appears that 10.11.2 has fixed it. This was the first time I had an update go bad, thankfully. Communication would go a long way, but results are always appreciated. I still feel they (Apple) are the best horse in the race. BTW here is the Apple Support thread on this; https://discussions.apple.com/thread/7252069?start=0&tstart=0

From https://support.apple.com/kb/PH21782:

OS X El Capitan: Set your Mac to log out when not in use

You can set your Mac to automatically log out the current user after a set period of inactivity. This helps ensure that your information is secure when your Mac is unattended.

• Choose Apple menu > System Preferences, click Security & Privacy, then click General.

• Click the lock icon to unlock it, then enter an administrator name and password.

• Click Advanced.

• Select “Log out after... minutes of inactivity.”

• Set the amount of time before the user is automatically logged out.