There's a useful article from the RHS on clematis wilt:
https://www.rhs.org.uk/advice/...
I had it happen here with a clematis that was planted close to the house so that it could climb up supports. Every year it would be just about to flower and then collapse with wilt. As far as I remember, because that part of the garden was sacrificed for a house addition so this is a few years back, one year I cut it off at soil level and mulched it and after that it was OK. I regularly see some similar clematis at a local garden I am familiar with where the roots are in the shade away from a building and the tops climb through shrubs and fencing into the sun. I've never seen wilt on those.
