It may be a silly question, but are they getting enough water?

That would be my question too... and, were they well enough watered last year?

The horse manure - where did it come from? Was it bought from the garden centre, or supplied by a local stable?
Did you use it elsewhere in the garden too, or just in this bed? If just in this bed, when did you apply the horse manure, and when exactly did you plant the shrubs?

I'd also ask whether this particular bed is much more open or exposed than any of the other planted areas?

The reason I asked about manure and whether you'd used it elsewhere without harm was in case it was contaminated with aminopyralid, or hadn't been composted properly or for long enough. You've said it comes from a local stable, which is risky, but if other plants are fine where you've used it, its unlikely to be that.

You've also said that 2 of the plants have 'wilt'. Wilt only affects hybrid clematis, not other plants, although there is something called 'Wilts' which is an umbrella term. Could be phytophthera infection if the top branches are hanging over in the shape of a shepherd's crook, and that is sometimes described as 'wilt' even though its not. That, though, is not what you've described.
As the plants are new, you may be able to persuade the suppliers to replace them, but the problem, if the bed is exposed (which you have not told us), might just be that the cold weather kept nipping the new leaves all the time.