OK, further research. Here's a very extensive discussion of the autostartup "feature"/issue (and problems it's causing): https://www.tenforums.com/general-support/95776-restart-fall-creators-update-reopens-apps-before.html. There is a workaround, a bit inelegant, but it does appear to work. Right click on the desktop, choose "New", then "Shortcut", then enter: shutdown.exe /r /t 0 . Then "Next", then name the new shortcut, "Restart". Then right click on the new shortcut, choose "Properties", then "Change icon" button, then select an appropriate icon (I chose a blue curved counter-clockwise arrow). With this specification, this shortcut restores the old pre-Fall Creators Update behavior of shutting down all programs during restart. You can rinse and repeat to create a "Shutdown" shortcut using the command, shutdown.exe /p .
Windows team: This is a pain in the neck, and a dangerous feature. As someone in the above linked forum noted, re-opening open applications is not acceptable if you're working on confidential material. There needs to be an option, or at least a Registry edit, that re-establishes historical behavior.
Resilio Sync team: Why do most other backbground programs appear to terminate during a shutdown or restart, but Sync doesn't? Can Sync be modified to terminate automatically notwithstanding Windows' new "feature"?
Some further similar info here: http://www.winhelponline.com/blog/stop-auto-reopen-programs-restart-windows-10/.