I had the same problem yesterday 02/06/2020. I had internet connectivity as well as my other PC’s on the same network. I checked the remote access option on my Plex Windows Server which, was indeed disabled. I shut everything down just for the heck of saying I cold started everything. Still no good. I gave up after about 45 min. of researching possible solutions on the web. I left everything on. Mysteriously I came back 3hrs later and everything was fine. WTF!!!