Latest news on this.
First of all. The Microbit Comports will not be visible in the Control Panel Device Manager until they are used.
That's a new behavior. So don't worry if you don't see them directly after an installation. They will show up when they are used.
Secondly. I found that a clean install works fine.
However an update from a previous version 1.6.1 or older has an error.
This will be fixed in later releases. This error can be solved quite easy by following this procedure.
Workaround:- Before installing. Uninstall the previous version. (This will not remove your settings).
- Install the new version. You will get a complaint about a missing dll when you start.
- End the program and install again (don't uninstall before doing that).
- Now everything should work