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Here is an article on how to prune a bird of paradise that will guide you:
https://www.gardeningknowhow.com/ornamental/flowers/bop/bird-of-paradise-pruning.htm

Usually when someone describes a "white film" it is powdery mildew. Here is an article on powdery mildew that will help you:
https://www.gardeningknowhow.com/plant-problems/disease/powdery-mildew-homemade-and-organic-remedies.htm

The bird of paradise will not survive temperatures below 50F. For this reason, I would recommend that your bird of paradise be outdoors only during warmer months. Here is an article that outlines the care of bird of paradise plants:

https://www.gardeningknowhow.com/ornamental/flowers/bop/bird-of-paradise-an-exotic-flower-like-none-other.htm

Happy gardening!

Here is an article that will help you that discusses how to eradicate mealy bugs:

https://www.gardeningknowhow.com/plant-problems/pests/insects/mealybugs-control.htm

Happy gardening!

This happens due to too little humidity. If you can increase the humidity around the plant, it will help. Many people like to set the plants on pebble trays filled with water to help keep the humidity around the plant high.

I did some more research on this and I would recommend that you treat the plant for thrips. Thrips are a small pest that typically attacks the base of flowers or new growth. They will kill the flowers before they are able to open. A treatment of a general pesticie will clear them up. Here is more information on them:
https://www.ctahr.hawaii.edu/oc/freepubs/pdf/IP-9.pdf

Yellowing leaves can indicate a watering issue, either to much or to little.

Also the stress of repotting and a change in light and temperatures has likely added to it's stress.
Bird Of Paradise to prefer to be root bound and are quite happy in the same pot for several years.

Here is a link to refresh you on the care requirements.

https://www.gardeningknowhow.com/ornamental/flowers/bop/bird-of-paradise-as-a-houseplant.htm

Shorter blooms are likely due to more sunlight. Taller flower spikes will grow on plants in a shadier location.

Here is a link with more information.

https://www.gardeningknowhow.com/ornamental/flowers/bop/bird-of-paradise-an-exotic-flower-like-none-other.htm

Though the Bird Of Paradise like to be slightly root bound, if your plant is bursting through the pot, it is time to repot.

If left in it's current state the plant will likely become stressed, have lack of nutrients and may not flower.

Choose a new container that is a bit larger, about 2 inches. Make sure it has good drainage holes.

Here is a link that will help you.

https://www.gardeningknowhow.com/ornamental/flowers/bop/dividing-bird-of-paradise.htm