Logged in and tried to see if it would work on my Hisense 43H7C. Didn't work. The Plex logo came up and nothing happened for about 2 minutes and then I get a notice that it didn't work and to reset the app. Reset it, also deleted it from my plex devices and retried it. Still didn't work. It doesn't even show up in my devices list. It at least did that before even though I'd get the "not available" notice. I don't even get that now.
I am getting the exact same issue. I have a Hisense [50DU6070] 4k 50in Smart Tv. Everything worked fine last night (the last time I used Plex). But as of right now I can't even get into Plex. The app starts up, I see the giant PLEX logo, but then nothing. It stays on that logo for a long time, then I get the following message:
"Plex is unable to start due to an error. Please start by using the Reset Plex button below, which will restore your default app settings, after which you can link to your Plex account again. If you continue having issues, please drop by our forums at ..... and tell us about this in person."
I have clicked that reset button 5 times now and I still get nothing but this message. I really hope you can get this fixed soon. I used Plex almost exclusively on this tv for watching my shows.