I'm having problems with my Brunnera 'Jack Frost' - the leaves become covered with brown spots in July and August when the weather is hot and humid. The plants are in dappled shade.
It is probably a fungus. I have found that these plants do well in terrible soil, but really, really thrive in well-drained. Those in a raised bed do even better. In this case, it might be too much rain and the humidity. Replant it in a raised bed, give it a hit of compost and live in hope. It's a good plant, although one Brunnera to be wary of is B. 'Langtrees' - it has a pretty variegation but will spread everywhere.
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