Exactly what it says: The game is still under development and not all content that's in the game right now is complete. When it comes to quests, the game will give you that warning to let you know that you've done everything possible right now and a lack of progression isn't due to you missing anything, please wait for it to be updated at some point in the future.
There are a few quests right now that are in that state and will likely remain there for some time (largely ones connected to main story content) so don't be surprised if you've done everything doable and still have a number of quests in your Current tab.