My default router settings use 192.168.0.1. All of the devices in my house can connect to the internet and the gateway when the IP range is set to default except for my Ubuntu device. My ubuntu device cannot connect to the gateway at all and intermittently loses connection to the internet.
If I change the IP router settings to the 10.0.0.* range, my Ubuntu device can connect to the gateway and no longer has trouble connecting to the internet.
I have scanned to see if any apps are bound to the IP or port 80/443 but come up with nothing.
One thing that I did notice is that if I disable IPv4, my IPv6 cannot connect to the internet at all. Sorry, I don't have the experience to know whether or not that is relevant.