I'm talking about, when you go solo in a level, the level becomes restricted so no one can join you (until the next depth).
I understand why this is implemented for lucrative levels. But sometimes levels I assumed wouldn't be restricted end up restricted, and vice versa. Would being in a PUG versus a friend group before you go solo make a difference as well?
Is there a comprehensive list/page/explanation as to which levels become restricted once you go solo?
It becomes restricted whenever you hit "Lock Party" on the far left party options.
The only exception is the boss levels.