Clematis help please!

[WheresMyClint]

I purchased several clematis from a reputable retailer this year and all have been doing well. Two of them, Clematis Koreana Broughton Bride, flowered beautifully but are now looking very unhealthy. All the others are still looking great. I emailed the retailer to ask for some advice, not to complain, and was told that as I'd used well rotted manure as a mulch this had probably damaged them, no further advice was forthcoming. I've added pictures to see if anyone here can help as all over the internet, including RHS etc says that well rotted manure is fine to use as a mulch for clematis. Just to say, the gravel boards sit on the ground, there's no concrete below the soil drying anything out etc. Thanks in advance!

Could that be scorch from sun or wind ? Clematis like their roots in shade so is the soil there very exposed ?

I'm no expert on clematis but I found this on a website:
"They do not need the 'rich' growing conditions or deep planting that the large flowered cultivars prefer. Because they have very fine root systems they will not thrive in soil which is prone to water-logging and they will actually be happier in poorer soils with very free draining conditions. If required, prune immediately after main flowering. Avoid them becoming too excessively wet during their first autumn and winter in the ground or perhaps plant in the spring."

It sounds as if the general advice to add mulch to clematis does not apply to this particular one. Also, the very wet month of April may not have helped.

Thank you both. It's a north facing bed but the tops get sun in the late afternoon. I think it's possibly a combination of too fertile soil, plus the late frost and unusually strong winds we had. They won't flower again until September if they survive, so I might try moving them to part of the garden with poorer soil.