Hello guys

I have 3x Deco M5s, one (on the ground floor) is connected to my router (the router is in modem mode) and its the main Deco. The other 2 are in 2 different floors. Everything has been working great so far. However, I have connected 2x devices via ethernet to my Deco which is in the first floor and everything has been great but today I have been getting some issues.

The device which I have connected via the ethernet cable to my Deco in the first floor is a linux computer and I access it via SSH and it has a domain assigned to it from duckdns so I can access it anywhere I like. The ip address assigned to it by the Deco is 192.168.68.121, and what I have been noticing lately is that I can SSH into my linux via the duckdns address but when I try to SSH it through its ip address i.e. 192.168.68.121 it doesnt allow me (I am in the same WiFi network as my linux computer). 

When I restart my Deco which is in the first floor, everything works fine and I am able to SSH into my linux computer via its ip address as well as its duckdns domain. 

I have never experienced this before, can someone tell me whats going on with my Deco?

Thanks.