Server Version#: 4.12.3
Player Version#: 4.17.1
Tizen Version#: 2.4.0
Samsung UE49KS7000
Since the latest update to the Samsung app, Plex will not load directly from the Smart Hub. It will only launch if you open it from within the Samsung Apps menu. If you pin Plex to home it will not open. This behaviour only started after the most recent update to the Samsung Plex app.
After seeing the same behaviour with another app (UKTV Play) I tried resetting the Smart Hub (Settings->Support->Self Diagnosis->Reset Smart Hub) and this seems to have solved this problem.
Edit: The reset smart hub solved the problem for me, but it happened again the next day. Not to mention you lose all the apps you’ve pinned to the Samsung home screen
Same Plex app and Tizen version as OP. TV is UE55KS7000.