I'm not sure, but I'll look into it as soon as I can. Thanks for the report. Do you remember the other options you set when trying to make the league? For example, how many teams did you select to create? I might have a testing gap with certain combinations of options. I'll look into it.
I do want to caution against creating a large number of teams to fill 20 conferences, though. At this stage in the game's early access development you might run into large wait times in not only creating all of those teams, but it will also take a while to simulate games between all of those teams each week in career mode. I've been making a lot of optimizations in these areas lately, but more complex optimization techniques are going to be needed to support 20+ conferences with 100+ teams with reasonable wait times. The default league that ships with the game has around 50 teams, which is close to what I think is the current sweet spot depending on the specs of your computer.