If you are using Chrome and macOS High Sierra is logging you out, you can open up the Chrome web browser -> go to settings -> click 'Advanced' -> turn off hardware accleration. Or Preference -> Security & Privacy -> General -> uncheck the box 'Require password after sleep or screen saver begins'. If macOS High Sierra keeps logging you out of your Mac, you can just go to Preference -> Security & Privacy -> Advanced -> uncheck the box where it says 'Log out after …minutes of inactivity'. Make sure you have updated them before upgrade to macOS High Sierra 10.13. There are kinds of apps including Apple's own apps that won't be supported by macOS High Sierra if you don't update them, say Final Cut Pro X 10.3.4, Motion 5.3.2, Compressor 4.3.2, Logic Pro X 10.3.1, MainStage 3.3, etc. It is helpful for the Mac Mail problem as well. So, you have to update your 32bit apps to 64bit or just replace them with alternatives to solve this kind of problem. When it arrives in 2018 MacOS 10.14 will not support 32-bit apps at all, a little bit like the way iOS 11 doesn't support 32-bit apps. Some apps can't work with macOS High Sierra? Apple had said that apps sold on the Mac App Store should be 64bit from January 2018, meaning that Apple is moving away from 32bit apps.