The most likely cause of this would be that you haven’t ticked “Enable Timeline Callbacks” on the FMODAudio Component. It could also be that your Event has not reached its natural end, either because of a lingering audio signal (e.g. reverb, delay effects), because you have additional timeline logic in the future that has not executed, or because the event is set to be persistent.
I would recommend against creating a bank for each event in your project - besides your choice of which events to assign to a bank, FMOD will handle a lot of the optimization around banks at runtime for you, and offers API functions if you want specific bank loading behavior. Banks are comprised of audio sample data, and event metadata, the latter of which is comparatively small as far as memory goes. Unless you specify otherwise, when loading a bank FMOD just loads the metadata, and will only load a given event’s sample data when you create an instance of the event.
For more information, please see my reply here to another user asking a similar question:
If you have any further questions about how bank layout and loading work, feel free to ask.