Certified GKH Gardening Expert
They require a dormancy, and will start to lose their leaves when water is, properly, reduced. Yellowing should occur.
Seeing brown can be a sign of bacterial, or fungal infection. This happens when the soil remains too moist for too long, without a dry out period. This leads to the perfect environment for infection.
From here, you will need to let it finish out dormancy, removing any infected leaves. Do NOT cut the branches back until it is ready to go back out.
Treat with a fungicide, as well, then let it go almost completely dry to the bottom before watering again. Water sparingly, until time to break dormancy.
These articles will help: