Check your connections. I moved away from Bittorrent Sync because I couldn't easily stop it hitting external trackers, or if I did, sync stopped working completely (especially on the Android client).
It is possible to turn off the tracker and use "predefined hosts" instead - see details here: http://help.getsync.com/customer/portal/articles/1901264
Note that the "predefined hosts" must be able to access each other (once you turn off the tracker for a folder you also disable NAT traversal)