I have looked at this post (https://support.plex.tv/hc/en-us/articles/200288666-Opening-Plex-Web-App), and it says to do exactly what we did. Our ISP had maintenance that took us offline for about 12 hours, and even though my server is directly connected into my network as is my Roku AND the laptop (connected to a projector). Both stated that they couldn't access the Plex server because there was no internet connection. They're all connected to a router that is connected to the modem. I could still access all the devices through ping and FTP, but I couldn't get further than launching the Plex page and getting the internet error.
Is there potentially a configuration that I've missed? It seems weird that I wouldn't be able to access my own content on my own physical server from my own network without an internet connection. Kinda defeats the purpose...
As a side note, we're going to be travelling soon (RV), and won't always have reliable internet access (if at all), but want to be able to access our Plex on our local network we'll have set up.
Thanks!