Moisture issues or too much sun can cause this problem. Make sure the plant is well mulched with 3-4" of any type of acidic mulch. Then water anytime that the soil feels almost dry or dry to a depth of 4".

I have a camellia whose leaves reacted quickly to loosing the tree that provided it with dappled sun. They started to brown out so I had to protect them until later this Fall when I can move them shrub with less stress. Damage was limited to leaves in contact with the sun. These partially browned leaves will not recover but will remain attached to the stem until it is time for new leaves in Spring. Camellias keep their leaves for about 1-2 years.