The established plant is 5 years old. It bloomed about 2 months ago. It's in a pot that is kept inside during winter.
Bird of Paradise Leaves Are Turning Brown
Certified GKH Gardening Expert
There are a few things that could be causing this. It may not be getting enough light, humidity, water or could be in the path of a cold draft.
I would increase the light, set the plant on a pebble tray, make sure to keep it watered appropriately and check the area for sources of cold drafts.