After installing the Windows 10 Creators Update, a prompt to choose a new folder location for Box Sync appears. After choosing a new location, Box Sync re-syncs all of my files.
Due to changes made to the Box Sync root folder during the Windows upgrade, Box Sync no longer "trusts" the existing folder and will attempt to create a new folder. If the original Box Sync folder was installed at the default location (C:\Users\[username]\Box Sync), the folder creation will fail due to a naming conflict. This is why the "new folder location" prompt appears. Renaming the old folder and then re-syncing will solve the issue.