Samsung is notoriously bad for reusing model names on multiple products, but there are 4 products named the Tab S2. The best are from 4 years ago, the worst from 5 years ago. they all have 3GB ram, which should be more than enough for Roon (by a lot). If they are dumping Roon from memory, it means Android is being overly aggressive since it is expecting you to be using many apps. Try closing out (fully dismissing) most apps and see what happens… or if you are visiting the web browser, close out all your tabs. It might help.
As for the One Plus 5, it should have no issues… want to try the same thing and report back? try to take a video with another phone of what you are talking about exactly as well… maybe something else is going on…