I manage to get my first zyxel multy x up and running, but not to get the two other up an running

Hi @ursusbjorn ,

Please be aware that the Multy X model has reached its End of Life (EOL) status, which means our support for this model will be limited.

We have sent you the latest firmware version V2.20(ABKJ.8)C0, along with the update instructions, via the Community inbox. Please take a moment to review and give it a try.