Originally Posted by Shagjitsu

Hey, All,
As of this recent maintenance on 2016-10-06, 2-1 isn't spawning any special bonus levels anymore. Is anyone else seeing this? Did they just drop the spawn of the secret levels?

-Shag

You probably had an expired bonus stage sitting there.
If you have one gray bonus stage , you won't get any bonus stages of the same difficulty as long as that stays there.

To remove it you need to reload the game/page , then you will be able to get more bonus stages.
That's the only way.