Thanks to further analysis of Joost, the problem seems to be in the Zyxel firmware, not in Ubunt / Linux: problem occurs after changing the default SSID name to something else. See https://forum.telfort.nl/pilots-feedback-273/ipv6-p-2812hnu-f1-wifi-dad-33361/ (warning: Dutch)
Thanks to further analysis of Joost, the problem seems to be in the Zyxel firmware, not in Ubunt / Linux: problem occurs after changing the default SSID name to something else. See https:/ /forum. telfort. nl/pilots- feedback- 273/ipv6- p-2812hnu- f1-wifi- dad-33361/ (warning: Dutch)