@TP-Link_Deco 

Did the laptop connect by Ethernet cable or by Wi-Fi?

Wi-Fi

During this time, is there any change on the LED light on the Deco, like green, then red?

No red light, no one else seems to have this problems but me.

Did the issue happen to laptop and mobile phone as the same time?

It does, but it doesn't affect my phone as much. When my laptop is "connected" to the deco and internet says "available" it's not able to load anything for 5 to 10 minutes. My phone's internet freaks out a little bit, like a minute or less when this happens. I tried to leaving it as is in the laptop to see if the issue resolved itself and it did after the time i specified before, but just today i did that, the issue resolved itself and then in crashed again. Again my laptop was the only one to lose connection as my brother's desktop seems to be fine, and this time the "default gateway IP" was lost and the troubleshooter (on my laptop) had to reset the Wi-Fi adapter to fix this. As soon as this happened i instantly got working internet again. During this second internet loss today, i lost connection to the deco for a bit, but i think it was just for the app being inactive for a while. Both these internet errors happened in less than 25 minutes and now im writing this reply. I might think this could be my laptop but it's highly unlikely as internet worked fine before the Deco devices got installed and i seem to be able to connect to the router directly just fine.

And when the connection dropped, are you still able to open the Deco APP and check the advanced>internet settings to see if the IP address is still here？

By the way, how long have you had the Deco and when did this issue start?

IPV4 seems to be there and IPV6 is disabled.