Hi Appletvgk,
My server is set never to go to sleep, is your's set likewise? Yes
How are you interact with your server?
I set it up using USB connected peripherals. Now it's headless without anything connected.
Do you have a bluetooth keyboard/trackpad/mouse?
I didn't set anything up, BUT I didn't disable the feature that turns on BT if no KB is plugged in. I will turn this off and see what happens.
Stop your Screen Sharing/VNC to your server, and wait for all of the timeouts to occur (logout, screen saver). Reconnect using Screen Sharing and see if your server is screen saving. You might also switch the System Preferences -> Sharing from Screen Sharing (uncheck it) to Remote Management (check it and setup for only your account to have access), and then retest.
I will try this but I'm at a remote location. I take it there is a way to SSH in and turn screen sharing back on? Otherwise I can't get back in.
Do you have "wake for wifi network access" set?
I think it says "wake for network access" on mine, I have it turned on. Maybe I should turn it off since I have sleep set to "Never"?
I notice that my MBP has a tough time going to sleep if this is set -- perhaps it also interferes with the logout? You might also switch off Power Nap (on your server, it's probably not on) so that it doesn't do any Time Machine backups, just as a test.
Time machine is disabled, because it would interfere with my databases (back up open databases and you get corrupt backups).
And finally, as I'm sure you have already thought of this, but switch off your web server (and/or database server) to test if the machine will then logout your account or screen save.
Actually I didn't try turning off my database server because I'm trying to keep it "up" for people to access, but I also don't "think" it's that because I ran the same server on my home mac without these symptoms.
Switon
P.S. ...really, I'm just fishing for any cause that might hinder your auto logout or keep your screen saver from starting...if you are connected via VNC/Screen Sharing, this will do it, but you have this problem even when not attached...