Abhishek,
Dixit is correct. Banana missing core is due to stem borer.
Banana farmer here use a deadly poison. with every emerging new leaf they add a small piece of the chemical. This is where they get into the core area of the banana.
this is a common problem with banana farmers.
The reason you don’t see them is they have done their job some time back. check your exiting healthy banana you should be able to locate a borer. check the attached file.
