Thanks, @Underknowledge, but that did not work as well.
While then displaying the RPis processes at a second screen, a few more search suggestions came to my mind. In several threads (especially this: HassOS docker0: port1 entered disabled state - #4 by KKnishev) cases like mine have been discussed.
Well, I just bought a new SD card, installed hass.io on it and everything works fine. 