Fenix 3 won't update activities

I'm signed in, hook up the fenix to Connect, but the activities don't update. Even when I click the "sync" button, it tells me there is nothing to sync (though history on the fenix shows me there are additional runs in the queue) (by the way, this happens repeatedly. At some point the data will appear, but randomly nad it often takes days.) Seems like it should automatically download activities when it's hooked to the computer, but nothing's happening. Any insights anyone could provide would be appreciated. Thanks.