BitTorrent Sync must be locked into a mobile mentality... I was unable to get my Android media hub, which I connect to via ethernet working with BitTorrent Sync for hours, until I finally decided to enable Wi-Fi. Enabling and disabling "Use mobile data" had no effect, but because that setting was there I figured somewhere in the code, there was a check for Wi-Fi and/or mobile connectivity. Note, none of the many other apps which use networking have a problem with an ethernet-only device, and that includes Dropbox, Pandora, Rhapsody, and a host of email clients. I'll assume this issue will get addressed and fixed at some point in the future, because more and more non-mobile Android devices are appearing, and obviously syncing over ethernet is orders of magnitude faster than Wi-Fi.