bud of plant turning brown
Why are some of the flowers that are yellow turning brown on my houseplant Anthurium?
It is possible that you have thrips. They are hard to see and they cause damage to the buds like that. They can attack the base of the flowers and kill them before they open. This article will help: https://www.gardeningknowhow.com/plant-problems/pests/insects/controlling-thrips.htm