you need to downgrade your app to 7.27.1.15203 player version. Just download it from https://www.apkmirror.com/apk/plex-inc/plex/plex-7-27-1-15203-release/
First uninstalled the current plex app. Disable the google play store auto update and enable allow unknown sources to install apps from any location.
Just keep repeating the process until you find a correct Plex app version that works for you.
I hope this help. thanks me later 
