@IanK 

Thanks for the support David. Sorry for the delay in replying, See comments below, labelled <IK> 

You wrote-

Except for the logs, I hope you could check some other details: <IK> which logs should I be checking, there's so many! What should I look for in them?

1. the IPV4 address under Deco APP>More>Internet connection. <IK> 89.9.224.141

2. Would the internet restore if just unplugging/plugging the internet cable between Deco and ISP modem? <IK> I've not tried this yet. I will do when it next occurs. I happened again on Sat night and my daughter power cycled the main deco (and restored the internet by doing so) before I could get to it! 

And you could find a debug firmware for Deco M4 v2, It is suggested to install the debug firmware first and save the system log when the main Deco turned red again.

(Since reboot would erase the system log, please do not power cycle Deco before saving the logs.)

<IK> I'll install the debug firmware as you suggest. Is it just the system log I need to save if/when it goes red?

You could send an email to support.forum@tp-link.com with the above information if the disconnection started again.

<IK> I've got a case with ticket no. TKID230116149

Best regards,

Ian

  @IanK 

The beta firmware hasn't fixed it. We've had a crash about 30 mins ago. Plugging my PC directly into my internet provider's modem worked. Removing the ethernet cable from the router to the main deco and replacing it after 10 seconds didn't fix it.

the red light is solid on all 4 deco's. I can't connect to the deco's to recover the logs. I've switched the main deco of for 10 secs and back on again. All is now working again.

How do we diagnose further?

Thanks,

Ian

  @IanK 

hi

I have 3 S4 TP-links and have many issues:

At first I had them connected with the main unit as a router with the virgin Media hub in modem mode. Yet randomly every 1-3 months the main unit and all the other units turn red. I thought it was VMedia so I would reboot everything.

I use over 550GB a month Via a 500mb VMedia broadband service so to see if the TP links were being overworked I switched them to AP mode and wired other items such as the virgin tv stream box, PlayStation and Apple TV to the virgin box directly. This means that if the TP units went down it was only Wi-Fi and I could test if the broadband was still on via wired units.

So around month ago the units went red again. Most of my alexas went red and I knew the Wi-Fi was down. To test it wasn't the Virgin router I turned on the Playstation and it connected to PSN and was online all fine.

So why did the TPlinks turn red? I initially followed TP link support advice and pulled out the network cable but this did nothing. Only a 2-3 min switch off and on fixed the units. I even had to reboot a backhaul extra unit as wouldn't reconnect.

TP- link support were great and via an RMA they swapped the unit costing me around £20 in posting and admin charges. 
 

For the laSt two weeks these have been fine. Until tonight! 2+weeks after installing the new units tonight they have gone red again and once again the virgin media broadband is fine with me able to use wired broadband.

So why have the new units now failed again? A reboot and they are back online again. But Why Why Why do they randomly fail?

No network loops, I use a TP link 8 port metal switch but this works fine. It's like an extension lead.

Is it worth rebooting the main Deco every week via a timing plug? Do these units get a memory leak or fault after 2+ weeks of usage? 
 

I don't want some more units with another RMA. I simply want to know why they randomly fail. 
 

It's better in AP mode as you only need to reboot the main unit if the VM broadband is fine. 
 

I understand your grief. It's a random issue but it a pain as a lot of my smart devices rely on these units.

I hope this helps, it did me to know that although you have M4 they are almost the same units. 
 

If you or anyone else has a fix please say. To me it's a device issue that I don't think it will go away.

(My units have latest firmware as they automatically updated when installed.)

thanks.