If the update fails for whatever reason, then clicking in the systray on the update message will show this error (and the update does not start again):
2019-09-03 11:12:20 12434 139704270419776 WARNING nxdrive.gui.application A new version 4.2.0 is available. 2019-09-03 11:12:27 12434 139704270419776 ERROR nxdrive.updater.base Update failed Traceback (most recent call last): File "updater/base.py", line 120, in update self._install(version, self._download(version)) File "updater/base.py", line 142, in _download url = "/".join([self.update_site, self.versions[version]["type"], name]) KeyError: ''