Suddenly the Plex app in all my Rokus either cannot locate a server or play a video.

Suddenly the Plex app in all my Rokus either cannot locate a server or if it can find a server it will not play a video. I have been able to get it to work with Plex opened in a browser and the Plex app in my android smartphone. I have tried rebooting the server PC, wifi router and cable modem. What else, if anything, can I try?