Please Help - my hydrangea plant looks like it's dying!

I'm not sure what the problem is. It's only this one bush which is in a row of about 8 or 9 hydrangea bushes. All the others seem to be healthy.
The only symptoms are that some leafs have turned brown and there is this strange what stuff on a few of the green leafs. Links to pictures are below.
This is the plant directly next to the one is the above 3 images. It doesn't look as sick but there are some eaten leafs. Thought I'd post a picture for reference just in case.
Many thanks if anyone had some advice.
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