@ElJacko Hi, Really sorry for the inconvenience. I wish I has caught this post in the first place. We left for the new year vacation last week and did not check the forum frequently as usual. If you still had the Deco, I would be glad to provide further assistance, and you could email support.forum@tp-link.com with the following information:

1. May I know who is your SIM card carrier?

2. When 5G preferred is chosen, did Deco X50-5G still tend to use 4G a lot?

3. Could you please send some screenshots of the Internet settings page on the Deco APP?

By the way, may I know the model number of the Zyxel device?

Wait for your reply.

Thank you very much.

Best regards.