Why does High Sierra remove my Login Items? After updating to macOS 10.13.1, my Login Items have vanished. Some users have reported this behavior in earlier betas, but this is the first time I've experienced it in a release.

Is there a reason for this behavior. Is there a way to identify what items I had configured  so I can restore them?
I have lost all my login items too after upgrade to macOS 10.13.1.

You could take a look the plist file at ~/Library/Preferences/com.apple.loginitems.plist, it may still contain names of login items, then add them back manually. I recovered mine in this way.

I guess 10.13 has moved login items config to somewhere else but failed to migrate old ones.