Looks like you have everything right to me. Even the selection of variety for pot culture seems sensible. The main problems with pot-cultured bamboo are over- and under-watering. The latter can be due to the pot becoming so full of roots that there is no space left for soil/water, but you repotted to a larger pot recently so that shouldn't be a problem yet.

Greenfly are only an occasional pest of bamboo, the greefly usually have juicier pickings. So the heavy greenfly infestation may be an indication that the plant was already weakened. I wonder if some vine weevil grubs have been chewing the roots, or some other root ailment. Or if the greenfly brought in some rare virus.

The only other thought is that bamboos don't like strong winds. This kind of bamboo naturally grows in the understorey of forests, where it isn't very windy. I wonder if your balcony, although glass panelled, is some kind of very windy place.

I'm not sure if the culms are dead or merely defoliated. If the culms are dead, the plant might resprout from the roots next year. When the weather is Septemberish, tip one out of the pot and have a good look at the roots.