I'm sorry... just watched the video. To me, it looks like there is air trapped inside the PS120 housing which has simply not been evacuated, though it's hard to believe that it would not have been displaced by now. The videos I've seen showing incoming entrained air are more disruptive and typically show air bubbles surging downward into the body of the strainer... not the gently rolling air which is in the top of your chamber.

One thing you can try is to disconnect the housing from your mount and tilt it so that the air can escape, and then see if it re-accumulates. If it does not show back up, then you've been chasing a ghost.