The probing of ports tagged as greylisted with a manual Manager.Scan() is broken because the manager object keeps the already probed (and failed) ports still around in their associated MMDevices. The MMDevice must be untracked and removed if no modem object is created for it.
Fixed in git master, e9d0989ed069b2b6f3deea438ef390998286601f.
Use of freedesktop.org services, including Bugzilla, is subject to our Code of Conduct. How we collect and use information is described in our Privacy Policy.