When it falls after taking it out of the oven, it means one of two things:
First, the batter could be too wet going into the oven - and just the state of the banana could be making the difference, even with you following the recipe exactly. A ripe banana (some dark spots) is mushier (more available free liquid) than a semi-ripe banana. And humidity can also throw things out of whack when combined with a ripe banana. A dash more flour helps in a case like that.
Second, I don't depend on the precise time the recipe calls for baking. I test the center with a skewer or long tooth pick, and when it pulls out clean, I sometimes give it an extra minute or two just to be certain it has set. An old time trick is to turn off the oven, open the oven door, slide out the wire rack with the bread at the front edge, and let it adjust to the room temperature while hanging out the front of the oven. It makes for a hotter kitchen, but in the winter time, it's welcomed, and prevents falling.
"Food is our common ground, a universal experience." - James Beard