I read that Erwinia rot is supposed to cause these symptoms. I have a potted banana that did exactly what your plant does and i am suspecting it. Maybe the soil where these bananas are stays too wet or these bananas are stressed from something? For the water sucker to have grown up well elsewhere,it means its happy or it would probably not survive at all.
Overwatering could be the reason this disease took hold and if you are not watering as much your healthy ones,you should change your watering schedule to that of your healthy ones and hopefully they will fix
If Pseudomonas fluorescence is available to you,get and apply some,your bananas would benefit from its protective nature against rot and wilts.