hanabananaman

I have had similar symptoms that slowly got worse. My soil was slowly depleted and it took me almost a year to get used to fertilizing as much as bananas need, I kept mistaking overfertilizing or disease with not enough fertilizer. There are some good threads about fertilizer needs that I learned a lot from. I used some sulpomag a few weeks ago and it has helped a lot, much greener and faster growth. I have one sacrificial pup that I have hammered with different fertilizers now and then to test a diagnosis. It likes extra N every time, I still have much to learn about fertilizing but I think you should follow directions carefully with the sulpomag in that small container it won't take much. It might be good to fertilize lightly with almost every watering. The wiser growers here can help more than me these are just my amateur thoughts.
Good luck