xpander, thank you 110% for your reply. I really appreciate the help! Thanks for helping me understand that this isn't really a MATE issue, or at least doesn't appear to be one.
Since my original post in this topic thread, I've been trying many things to get the random logout behavior to go away. I have thought to myself over and over that this seems like a hardware problem, probably a faulty graphics card or something. I decided I would go buy a new gfx card soon. I also continued to hunt around in other possible directions, such as BIOS firmware settings and upgrades, and then kernel tuning parameters.
I can't confidently say that it's working completely, but I did make a discovery that made my home-built computer boot faster and perform better -- AND my gnome session has NOT CRASHED for over 12 hours running and heavy use! The change was that I added the "nomodeset" flag in /etc/default/grub on the line that reads: GRUB_CMDLINE_LINUX_DEFAULT="nomodeset"
After editing that file I called $ sudo update-grub
Then I rebooted into a much faster computer.
You see my computer is hand-built. Here is a summary of my hardware (output of `lshw`) => http://pastebin.com/r8mqdzzc
Because the problem seemed hardware related to me, I theorized that the issue might have had to do with ACPI functionality in the newest Linux Mint kernel (I hadn't been experiencing these problems before that upgrade). By using the nomodeset kernel flag, it signaled to the Linux kernel not to emulate a windows operating system's ACPI behavior when interacting with the BIOS/motherboard. Since making this change, I haven't had any problems. I'm hoping this trend continues! If I can go another couple days without a session crash, I'll consider the issue "solved", at least for me.
One final note: don't try using "acpi=off" as a kernel flag, as this has (accurately) been described elsewhere on the internet as a "nuclear bomb" approach to ACPI problems. I can confirm that using it is problematic, and may cause your computer to become unbootable until you reboot it and remove that option from the Linux kernel parameters from the grub prompt and also from your /etc/default/grub, etc.
xpander wrote:it seems to not be MATE related from the logs.
it seems to be either gnome-shell or cinnamon.
i see clutter errors, nautilus errors, zeitgeist and gnome-shell ones. those are not part of MATE desktop.
if the x fails with gnome-shell.. its probably the 3d drivers which fail to load it up.