@OptimusS5 

Hi, May I know who your internet service provider is? How about the model number of the ISP fiber box?

For now, it is suggested to disable the WiFi on the Fiber box first.

As for the auto reboot issues, Did you notice Deco turn yellow during the reboot?

Would there be any modifications to the ISP service recently?

Usually, it is very likely to be some newly added devices, like 6G or WiFi 7 mobile devices. Have you got any suspects?

Thank you very much and wait for your reply.

  @OptimusS5 

Hi, Thanks for the update.

If the LED was only red/green, Deco didn't auto reboot, while it still randomly disconnected from the Fiber service.

How about the internet connection type when Deco XE75 was connected directly to the Fibre ONU?

Is it Dynamic IP or PPPoE？Did you have both IPV4 and IPV6 enabled?

It also helps if you could help me check the IPV4 address when Deco XE75 was red. Would it become 0.0.0.0?

---You could save a copy of the system log when Deco was red and send both details to support.forum@tp-link.com(please add forum ID#738938).

At the same time, please also test the following suggestions:

1. connect the Fiber ONT to another Ethernet port on the Deco XE75.

2. Clone the MAC address of the bridged WiFi router-How to Configure MAC Clone on Deco if Deco fails to connect to the internet

3. Change the IPV4 DNS to 8.8.8.8/8.8.4.4-How to change DNS server settings on my Deco

For other suggestions, please also refer to Case One-Fix unstable connection when connected to the Deco network

Thank you very much and best regards.