Unlisted WebExtension not Updated

I uploaded an unlisted WebExtension to AMO and downloaded the approved/signed xpi, installed in Firefox Developer Edition (52.0a2). I then modified the version info in manifest.json and uploaded again. However, I can’t update my add-on even if I manually clicked the update button.

Is unlisted add-ons not automatically updated or unable to update through AMO? Should I specify update_link in the manifest.json instead?

Unlisted Add-ons don’t auto-update via AMO.