Those signs are usually associated with too dry or perhaps too much sunlight - they 'do' like shade or at least dappled shade.
I'm not sure about soil types, i have mine in thin poor soil and some in slightly more moisture retentive - the only time they've suffered is when they're too dry or too sunny.

Or check the compost for vine weevil grubs!

Thanks, those are both really helpful suggestions.

I agree with the shade, Strawb, but I also had that happen with a severe aphid attack. Be sure to check the crowns where the new leaves come out thoroughly.