frankraney wrote:
Are the other objects the same distance. Did you zoom to 120, and get to close. If you are minimum focus distance the camera will focus and if you move forward very slightly, no focus, or bad focus. Remember, long lens, shallower depth of field.
Try the app, hyper focal pro. Play with it to get the best focus with lens and aperture, and distance to subject.
Chg_canon has a great article, posted in his response.
I also have the same concern as Frank, you're possibly too close to the flower where the lens could not focus that close? It's hard to say from the edited version, but that might also be something to confirm.