Does it sound like my tablet has a problem that needs fixing or being replaced?

I bought a Samsung tablet, but the lock screen feature doesn't seem to work. If I am watching something on YouTube, as soon as an ad comes on, the lock screen automatically unlocks itself. I will also have the YouTube video in full screen, but as soon as the ad plays, the screen goes back to its original size. It's absolutely frustrating.

Does it sound like my tablet has a problem that needs fixing or being replaced?
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