This is caused by a fungus. I have had the same experience and never successfully cured this problem. Perhaps another member has and will have some suggestions to give to you.

Thankyou loosestrife2 . I hope there is
a cure somewhere.

This is caused by the very wet environment, too low light level & poor air circulation. Try to find a new location for it with dappled sun, rich humus slightly acidic soil, good air circulation. Don't plant it too deeply; top of rootball should be level with the surface.

Trim off the badly infected branches and let it regrow a new crown. A little sun & open air will cure this.

Thanks for that. Very helpful.
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