"There has been a lot of confusion and concern because version 4 of Express removed the sync button. The reasoning behind this change, is that when a wired device is connected, Express will automatically start a sync to Connect with a supported device. For ANT enabled devices, once the device is in range and detected, it will also automatically attempt to sync with Connect."
It'd be really nice if that were true, but it's not.
Assuming Express doesn't spend ages checking for updates and then fail to connect to the Garmin servers, it just doesn't find my device and it doesn't transfer data.
Before Express, everything generally worked fine with Ant Agent.
Either Express is an exasperatingly poor piece of software or it's far from obvious how it's supposed to work properly.