It tells me that i am one this level but
It’s not a bug
The level that the arrow is pointing to is not always the one to play next. Try finding other red dot levels around the map and play those instead. (Or type in the link: something like codecombat.com/play/level/sample-level)
If it was a bug, I think someone would have already noticed it already.
I think it’s pretty sneaky to add a level that you can’t get past that you have to subscribe for.