Clematis × triternata 'Rubromarginata' stems dying off

[ltrsouth]

Clematis × triternata 'Rubromarginata'
Have had it in the same spot for three years but it has never had a lot of stems, maybe four or five, but now it is down to one. What happens is the lowest leaves on each stem start to wilt and it gradually goes up right to the end. The actual stem is dried out and shrinks. The one remaining stem is a mass of flowers but I would like some advice please. Can it be stopped or do I need to buy a new plant?