The drainage seems to be fine. It's kind of close to a pool though. I thought it might also be chemical from the clorine. There is a couple of douglas firs close to it, two of them are starting to thin and die out in the middle which makes me think it is funga like vercillum root rot or something. This is very commom around here with douglas firs, they don't seem to do well in our hot and humid summer climate.
The dead branches and top was cut out of the magnolia by the HO and now it just has some some suckers left.