Router ports stop working

Dear fellows,

i am having a strange problem at home.

Let me first explain my configuration.

I have a r6400v2 router as main that gets the WAN from the ISP. It is PPPoE configured with a dynamic IP and user and password.

On it I have attached a security camera system (port 1) and another mesh router (TP-Link Deco on port 2).

I use the wifi from the second router and use the netgear as mains. Also the WAN to it goes through an UPS system for protection.

Everything has been working fine for some time now, but a week ago i was setting up a plex server that is connected to the internal Deco network. I added a port forwarding and updated the software anda few days ago i could not connect anymore the router through anywhere access remotely. I then attached a computer the router with a cable to find out it says - no valid ip configuration. I checked the internal deco router - it was not getting internet. Curiously enough the camera system with NVR that i have attached on port 1 was working just fine. If i dettach the camera system from port 1 and attach it again it does not work anymore. 

If i restart the router everything goes back to normal for a few hours then again any other port than 1 stops getting internet and the router does not respond to nighthawk app.

I have not tried how is the wifi since i do not use it and the network is hidden, but this is a really strange behaviour. 

I have not also tried resetting it, but if you think this could work i will give it a try. 

I am just trying to find an explanation to that bizzare behaviour. 

I also do not see the other ports attached on the nighthawk app (see the attached picture). Although i have 3 ports connected i see only one in the list and everything works fine as it is.

Thank you.