@Katieq 

Hi, can I have a picture of the error message with no internet access?

Did any Deco turn red when this issue started?

May I know who is your internet service provider and what is the model number of your ISP modem?

Thank you.

@Katieq 

Thanks a lot for your kind reply.

I noticed that you are still on firmware 1.1.8 and please try to update the Deco M4 to be the latest firmware first:

https://static.tp-link.com/2020/202010/20201009/Deco%20M4_V1_V2_200918.zip

In case the firmware did not make any difference, please help me check the following details as well:

1. How often did this issue repeat with one day, like 3-4 times per day?

2. Did Deco M4 work on the access point mode or wireless router mode?

3. When M4 lost the connection, did you have to reboot the Deco to restore the internet connection?

4. Could you please log into the web UI http://tplinkdeco.net and help me save the system log on the web UI;

Thank you very much.

@Katieq 

Hi, Did your internet service provider offer both IPV4 and IPV6 connections?

As for the firmware upgrade, would https://tplinkdeco.net help or not? (https not http)

What would happen if you try to ping the LAN IP address of Deco?

Please also try to turn off the firewall on the computer to have a look;

Thank you very much and wait for your reply.

@Katieq 

Did you try both HTTP and HTTPS log-in?

As for the ping test(https://community.tp-link.com/en/home/forum/topic/264236?replyId=597682), since there are the replies from IPV6 address, I wonder what this IPV6 address is, the IPV6 gateway, or the IPV6 DNS?

Did the mobile phone or laptop get any IPV4 address, such as 192.168.68.xxx？

Or what you can get if trying to ping 192.168.68.1?

Thank you very much.

@Katieq 

Hi, Thank you very much for the update.

Please feel free to update here with any improvement and I will check here all the time.

And It would also provide some guidance for other users.

Thanks a lot.