Yes. You got it right. Although, I don't think so but still asking, do I need to setup port forward on the modem. (Zyxel) as well? I never faced an FP problem.
There is an inverter that takes care of power fluctuations or outages so that is covered.
Even on the ping -t 8.8.8.8 window I did not see any request time outs yesterday when it happened. But I am very clueless as to why it is happening.

Maybe I am chasing a ghost.

hi were do you have it set up?
are all routers in the same subnet like: 192.168.1.0?
the zyxel thats your log in to the isp. that should be were its dhcp server sends ips to the rest of your network. thats were you port forward, no were else. the other two routers are just "slaves". on those turn off their f/walls. apply/save.

I have always had it setup on my router(JNR) and not the modem(zyxel). I never accessed the modem page anytime.The access point was recently added like 5 months ago, but this setup has always been like that for almost 4 years.
This is the result in ipconfig /all when connected to the Access Point (WNR)

Wireless LAN adapter Wireless Network Connection:

Connection-specific DNS Suffix . :
Description . . . . . . . . . . . : DW1501 Wireless-N WLAN Half-Mini Card
Physical Address. . . . . . . . . : C0-CB-38-7F-A2-E7
DHCP Enabled. . . . . . . . . . . : Yes
Autoconfiguration Enabled . . . . : Yes
Link-local IPv6 Address . . . . . : fe80::ac54:e953:5bdb:fe2a%12(Preferred)
IPv4 Address. . . . . . . . . . . : 10.0.0.3(Preferred)
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Lease Obtained. . . . . . . . . . : 20 May 2018 07:02:24
Lease Expires . . . . . . . . . . : 21 May 2018 09:13:00
Default Gateway . . . . . . . . . : 10.0.0.1
DHCP Server . . . . . . . . . . . : 10.0.0.1
DHCPv6 IAID . . . . . . . . . . . : 314624824
DHCPv6 Client DUID. . . . . . . . : 00-01-00-01-21-56-CC-46-F0-4D-A2-9F-37-45

DNS Servers . . . . . . . . . . . : 10.0.0.1
NetBIOS over Tcpip. . . . . . . . : Enabled

hi
i think you have the set up wrong which may account for your problem. the ip above is 10.0 etc. whats the ip of the zyxel, 192.168. i would think.
what you have or should have for best results, is a daisy chained set up. if you google daisy chained you will see what i mean.

Oh! I see what you are trying to say.

Let me try configuring that, and will be abck.

hi
ok

Okay so, I removed the zyxel modem, and the JNR router, and replaced it with a D-Link modem+router model 2730.

Then I configured port forwarding on it. See attached. Then I ran voobly network diagnostics and results were positive. See below.

This used to return me warnings found, but now it is all positive.

Starting networking diagnostics...[You must login to view link]

Your local network port (UDP) is 16000. All game traffic is routed through this port. This can be changed in "Settings" -> "NAT Traversal".

Attempting to connect to 3 test servers. This will take around a minute to complete...

Received data from 'server 1' through port 16000 (this is your WAN or router port)
Received data from 'server 3' through port 16000 (this is your WAN or router port)
Received data from 'server 2' through port 16000 (this is your WAN or router port)
14 seconds left.
9 seconds left.
4 seconds left.

Test Result: All Pass
Network Health: All tests passed
Recommended Action: None
Details: All tests passed.

For help understanding this report or for more information go to http://www.voobly.com/pages/view/177#Network_Diagnostic_Tool.

After that, I configured my access point WNR2005. I could not setup in daisy chain mode, because it was asking me for primary dns and etc which i did not know.
Again after connecting to access point I ran network diagnostics, and results were the same. ALl positive.

Does it sound correct?

I will monitor it for some days, and hopefully this should solve it.

hi
ok
not sure why it needs dns for WNR2005. to set it up as a chain, turn on the dlink dhcp, apply/save.
log in to the WNR2005 open its lan page and give it a new private ip in the same subnet as the dlink[ ie: 192.168.1.251] [which should be outside the range of the dlink dhcp] turn off its dhcp. turn off firewall. turn off upnp. on page that shows type of connection, use the drop down to set it as "ether net or bridge." apply/save everty time a router page is altered.
the wi-fi remains the same.
now the dlink conducts all connections.
or
try your set up and see.