How to reproduce:
- load a savegame with enough money
- create new bases until you can't build more (after the 8th normally, if you didn't build any bases since gamestart)
- now exit the current game
- reload this savegame or any other
- -> the "Create Base"-Button disappeared, although you don't have 8 bases
How to get the Button back:
- restart the game or
- start a new campaign
(My) Conclusions:
Looks like the counter for max bases isn't reset after loading/leaving a savegame...