Posted: 16/05/2017 at 22:20
From what you've said, I think it's probably dry, and the roots aren't able to support the top growth as it will have put on that growth very quickly in the early warmth. Also, did you water it well and make sure the roots weren't tight when you planted it? Apologies if you've done all that, but sometimes the simplest things can cause issues.
Young, tender foliage is very vulnerable to any sudden changes in temp too, even in a mature plant of any kind, not just clematis. Have you checked to see that the soil it's in isn't dry further down? It's surprising how quickly a pot will dry out, especially when there's other planting in there as well.
To be honest, I'd have said cold wind or frost too - the appearance is fairly typical of that, but if you think you haven't really had any then that's fair enough.