Black aucuba leaves and stems

Me again, I've had a busy week! Can anyone tell me why Aucuba leaves suddenly turn black/brown and die off? It seems to happen to some branches on some plants and I don't know why. It can happen when it's been wet or dry or when the plant is young or old or when the plant is in the sun or shade so no consistent reasons as far as I can see. And I can't find a definitive answer online. I see it in neighbours gardens and get asked about it and feel silly when I can't explain something that seems simple. It looks like extensive frost damage but I've seen it suddenly happen in June. Help?? Many thanks. turmeric
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https://forum.gardenersworld.com/discussion/1015446/aucuba-black-leaves