So it's rare, but if there's a piece of bread stuck in the bottle cap that's outright Chometz. Are you going to start telling me it isn't a problem because the bottle is upright?
For the last time, b'ein literally means visible.
There is no reason to be concerned about a piece of bread stuck in a bottle cap.
That depends how you define visible. A wheat kernel mixed into a sack is visible but not discernible and is batel b'shishim.
Bottom line is that there is no real concern of chometz bimashehu in a soda production which would require tmidi.