Maybe you should be asking Samsung why your Galaxy S6 tablet doesn't switch between portrait and landscape viewing modes in the same way your previous Galaxy S2 model did. They might be able to point you to some specific user setting options that cause the S6 to act thay way.
If Samsung can't come up with any reason explaining that behavior, THEN you should ask Spectrum if they made a deliberate change to the app software. Of course, the Galaxy series is an Android device, so you might also have to ask Google who keeps upgrading and modifying their OS package.
Thanks for the reply. The tablet does work correctly in changing from portrait to landscape and back again on all other programs when rotating the tablet. It's only when I go to Live TV in the Spectrum app with the channels listed on the left and the preview on the right. In this view, the program will not go to landscape when the tablet is rotated. But when I click on the [ ] icon, the preview goes full screen and rotates to landscape.