Can't access device behind Double NAT LAN

I've got a few devices on my LAN running different Linux distros: * Ubuntu 20.04 * CentOS 7 * Fedora 33 They're all in the same subnet 192.168.50.0/24. Network map:  Until recently, from my PC (192.168.200.0/24) I was able to access (ssh,http) all three devices. The other day, I restarted the ubuntu box due to a prompt from the motd. After the restart I wasn't able to access (ping,ssh,http) into the ubuntu box any more. However, I can still access the ubuntu box **via** the other linux boxes. ie. Login to the centos box; Then login to ubuntu box from the centos box. What I've found out is if I run a **vpn tunnel** (wireguard server is on the ubuntu box) I was able to access this device directly without going through the centos box or fedora box. Apart from the fact this device acts differently to the centos box and fedora box, what can I do in terms of routing that allows me to access this device directly without running a VPN tunnel? Thanks everyone ---------- **Environment** * OS: 20.04.2 LTS (Focal Fossa) ---------- **Debugging Results** Routing tables

ubuntu # ip route show
default via 192.168.50.1 dev enp3s0 src 192.168.50.2 metric 202
10.6.0.0/24 dev wg0 proto kernel scope link src 10.6.0.1
192.168.50.0/24 dev enp3s0 proto dhcp scope link src 192.168.50.2 metric 202
192.168.50.1 dev enp3s0 proto dhcp scope link src 192.168.50.2 metric 100

centos # ip route show
default via 192.168.50.1 dev enp4s0
192.168.50.0/24 dev enp4s0 proto kernel scope link src 192.168.50.3

fedora # ip route show
default via 192.168.50.1 dev enp3s0 proto dhcp metric 100
192.168.50.0/24 dev enp3s0 proto kernel scope link src 192.168.50.4 metric 100