I've filled 4 islands but the 5th hasn't appeared. What do I need to do?

We already have an answer for a similar question which you can see here:
I’ve filled all 4 islands so can’t purchase anything, nowhere to put..

If you have more answers to add you can do that below.

If you've completely removed all the clouds from the 4th island and the map still does not show a 5th island, see if there is a game update. If game update doesn't help, contact customer service through the "help" button in the game settings (green gear icon).