After earning your points you should log out and then log back in immediately to check your status. I've noticed that when the points disappear they seem to do so right away. No need to wait until after the round is closed to log back in and find out that your points have gone missing.

I watch all the videos, vote, log out, then log back in. Roughly two times out of three the site will show that I've watched fewer of the videos than I actually have. So, I watch some of the videos again. Rinse and repeat: eventually the videos and the miles seem to stick.