Jul 23, 2016, 16:2907/23/16
@TestZero44 (23 July, 2016, 4:29 PM UTC):
They may have overlapped with one another.
To solve this, enter your sector edit mode and move your banks around to see if another one appears.
If you are certain that you have built 3 banks, and still can't find the third, contact the Help and Support Desk.