A level / island that should be unlocked is inaccessible due to being hidden behind clouds
The island has not generated yet.
Typically this issue will be resolved by allowing the the game to idle for some time.
This issue is due to a quirk in the way that our levels generate, that can cause them to keep on failing for quite some time until they find a playable level. We’re looking into finding ways to reduce / mitigate this problem.