Firmware version June 2022: I had contact with Zyxel support in June 2022, who provided me with firmware version V5.17(ABPC.2)C0. Here is the link to download it: https://www.dropbox.com/s/c0vzn7sm6z4vo9q - Unfortunately, I cannot prove that this firmware is legitimate. However, I have been using it and it has been working perfectly since June. According to support, the version is ONLY compatible with the generic version of the router (recognisable by the C0 at the end of the firmware).