This may or may not be a bug. It could just be bad game design and would therefore be a wish list thing. I say that because there are some missions that are on a timer for how frequently they spawn. For instance the VIP charters you only get one to spawn every day. I mean the VIP ones too, not the Private ones (what most people have unlocked).
These missions could fall into that category. I also know that some missions are region based. It’s also possible you need to unlock more of the map to see the new missions if they exist.
There is simply too much missing information about how missions work in terms of their generation to determine if this is a bug or not. Even cargo missions, if you do them quickly enough, you can run out in a given area. Granted they do spawn more somewhat quickly (hours vs days).