@Gits 

Thanks for reaching out. I understand that after upgrading your Deco firmware, your guest Wi-Fi network only works when you are near the main Deco unit (M9 Plus), but you cannot connect to the guest Wi-Fi from your second Deco (M5) unit.

This issue may occur if the guest network is not properly enabled or synchronized across all Deco units, especially after a firmware update. Here are some steps to help you resolve this:

1. Check Guest Network Settings:
• Open the Deco app and go to MORE > Guest Network.
• Ensure the guest network is enabled.
• Double-check the guest Wi-Fi name (SSID), password, encryption method, and frequency (2.4G/5G) settings.

2. Confirm Guest Network Coverage:
• The guest network should be broadcasted by all Deco units by default. However, after a firmware update, sometimes settings may not sync correctly. Try toggling the guest network off and then back on in the app.

3. Reboot All Deco Units:
• Power cycle (reboot) both your main Deco (M9 Plus) and the mesh unit (M5). This can help re-establish the guest network across the entire mesh.

4. Firmware Consistency:
• Make sure both Deco units are running the latest firmware. You can check this in the Deco app under System > Firmware Update.

5. Network Mode Consideration:
• If your Deco system is in Access Point mode, you can choose whether guest devices can access your main network (this is disabled by default). In Router mode, the guest and main networks are always isolated.

6. Additional Features:
• You can also set guest network duration and bandwidth control if your Deco model supports these features. If you do not see these options, ensure your main Deco is up to date.

If you continue to have issues after these steps, please refer to the detailed FAQ for further troubleshooting: https://www.tp-link.com/support/faq/1460/.

Let me know if you need further assistance!

  @Gits 

Hi, it is suggested to refer to this post for more advice:

Reported Issue and Workaround: Guest Network works only on Main Deco

Best regards.