The router should be able to change the LAN IP as well.
Are you using an external router to provide internet connection to your RUT955?
If so, please check your wan IP, it should be in a different subnet, for instance.
WAN IP 192.168.15.1 --> LAN IP 192.168.2.14
If your main router is in the same network, you'll have an issue, for example.
WAN IP 192.168.2.1 --> LAN IP 192.168.2.14
In this case, you won't be able to reach websites.
Please let us know if it's your issue, if don't, can you please download a troubleshoot file and send to me in a DM?