Can't connect to plex webui

I have installed plex on my server and for some reason after moving I can’t access the webui using the local IP and plex port of my server. my router is the same the only difference is I’m connecting it to my new ISP’s router/modem. What could cause this?

Your isp router may not be serving up the same lan ip addresses via dhcp

Would turning of dhcp on the isp router/modem solve the issue since I don’t want to use it as a router. How can this be resolved?

It depends on your network setup. I use static ip’s for my home and dhcp for visitors.

Currently both are using dhcp but I’m only usig one as a router and i gave that router where everything connects to a static IP in that dhcp.