I've tried oldscribe's tip. That box has always been unchecked for me. But I keep getting logged off. It feels random. But most of the time, it's happened while I was browsing and/or downloading from a browser. Any browser. It's happened while using Chrome, Firefox, and Safari. It's also happened a couple of times using Photoshop and Illustrator. Maybe I should've stuck with 10.11. As bad as it was, it never did what High Sierra is doing on my Mac Pro 5,1. With 64GB of Ram. I've also tried tips, like deleting preference files. I also did a Disk First Aid under recovery mode. And it tells me no issues. But still "random" log outs. I've even reinstalled the OS. Huge pain in the arse. But still same issue.
The only thing I can think of, is that it maybe the firmware update I had to do, to install High Sierra on my system. My GPU which has been running fine under 10.11, also seems to be acting wonky. Every so often, I get black bars on some window items (files/folders and their info). Closing the window, and re-opening fixes the issue. Until it happens again. Unfortunately, I can't upgrade higher than 10.13.x. I don't have a compatible Metal capable GPU. Anymore tips would be greatly appreciated. Thanks.