Home PC keeps disconneting from internet

I have two routers at home.
The 'main' one is connected to internet (92.168.1.1), has Wi-Fi and my desktop PC (192.168.1.10) is connected to it via ethernet cable.
Since the Wi-Fi signal is weak in my living room, I had second router (TP-Link Archer-C6 - 192.168.1.5) in the 'Access Point' mode. This means it is connected to the main router via cable and it just 'extends' the wifi (has wifi network with the same name/password). I had my NAS, TV, soundbar and Alexa connected to this second router. My phone and tablet is connected to my wifi and it changes the router dynamically based on the room i'm in. See the picture.
I have a problem with my computer though. Sometimes (I don't know the exact condition under which this happens) my computer lost access to the internet. For example I open a web page but after 5 seconds I'm disconnected. If I reconnect my network interface I got the connection again, but only for few seconds.
I'm not sure what can be the issue, but I think it might be that the second router DHCP interferes with the main router. But everything connected to the second router via cable (TV, NAS) has access to the internet and also my phone connected to the main router is capable of accessing external pages.
I haven't found anything interesting in my log files (Ubuntu 18.04). Here is the output of some commands during the time the connection is lost

root:~# ifconfig enp7s0; ip r; ping 192.168.1.1 -c 1 -W 1; arp -n; ping -c 1 -w 1 192.168.1.5 
enp7s0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500 
        inet 192.168.1.10  netmask 255.255.255.0  broadcast 192.168.1.255 
        inet6 fe80::fe4f:aced:12a0:9d12  prefixlen 64  scopeid 0x20<link> 
        ether b4:2e:99:3f:29:30  txqueuelen 1000  (Ethernet) 
        RX packets 938782  bytes 1168780050 (1.1 GB) 
        RX errors 0  dropped 0  overruns 0  frame 0 
        TX packets 454949  bytes 67960742 (67.9 MB) 
        TX errors 49  dropped 0 overruns 0  carrier 0  collisions 0 
 
default via 192.168.1.1 dev enp7s0 proto dhcp metric 100  
169.254.0.0/16 dev enp7s0 scope link metric 1000  
192.168.1.0/24 dev enp7s0 proto kernel scope link src 192.168.1.10 metric 100  
PING 192.168.1.1 (192.168.1.1) 56(84) bytes of data. 
 
--- 192.168.1.1 ping statistics --- 
1 packets transmitted, 0 received, 100% packet loss, time 0ms 
 
Address                  HWtype  HWaddress           Flags Mask            Iface 
192.168.1.1              ether   d8:7d:7f:b3:16:78   C                     enp7s0 
192.168.1.3              ether   00:11:32:b3:57:42   C                     enp7s0 
192.168.1.5              ether   cc:32:e5:78:0b:06   C                     enp7s0 
PING 192.168.1.5 (192.168.1.5) 56(84) bytes of data. 
64 bytes from 192.168.1.5: icmp_seq=1 ttl=64 time=0.346 ms 
 
--- 192.168.1.5 ping statistics --- 
1 packets transmitted, 1 received, 0% packet loss, time 0ms 
rtt min/avg/max/mdev = 0.346/0.346/0.346/0.000 ms

Please note that there is not much to set up on the second router while it's in the Access Point mode.
I can also ping both routers from NAS (ping 192.168.1.1 works fine) Do you have any idea what could be the problem? Or how can I get more information? Thanks

Home PC keeps disconneting from internet

Solution 1:

Make sure of the following 3 points:

Wireless Router LAN port to main Router LAN port.

Wireless Router to have Static IP on the main network.

Wireless Router to have DHCP turned off.

The static IP prevents the Wireless Router getting lost if it gets a different LAN IP.

DHCP OFF on the Wireless Router prevents 2 DHCP servers. This is very important.

Set up as I suggest, restart both routers and all should be well.

This is how I have hooked up here.