Re: Leagues filling

If it shows only one opening in a league, click 'Browse the League' and then click 'Schedule': any team that doesn't have a starter listed for the opening day matchup most likely hasn't completely drafted their roster, in which case their team gets bounced shortly after the league 'fills'. That's probably the situation you keep running into.

You can also click on each team's roster, one at a time, to make sure they have 23 players. It's a lot more arduous but sometimes worthwhile homework as you can see how different owners have put together their teams.