Brown buds on your camellia that are more on the outside of the plant and not the centre of the plant are often caused by exposure to cold frosty and windy weather in the winter that’s causing as the buds form or start to open. It sounds as though the plant it growing in a frost pocket or an area than catches the winter winter. As i
ts in a pot I would I would try to move it to another area which is less exposed if possible.
Where the browning of the buds is more on the inside it tends to be dew to a lack of potash and iron in the soil or compost if the plants been grown in a pot. The simple solution for this is to feed the plant with liquid tomato feed which contains both these nutrients in a soluble form