Over-fertilization? Incarnata are adapted to survive in poor soil, and too many nutrients can encourage vegetative growth at the expense of blossoms.

Other problems may be not enough water or the opposite end of the spectrum, poor drainage. Since yours sounds like it's growing fine, I suspect these latter two unlikely.

If it has not bloomed more than that in 3 years, I would shovel prune it and get another one. Incarnata are weeds and usually bloom easily under a wide range of conditions, so you may just have a bad one.

It has bloomed the past two years, but now with only one bud.

I have the same problem.My incarnata vine is huge and healthy but only had two buds that started to open,then died.We've had a huge amount of rain this summer,so maybe that's the cause.

wow thats un usual mine blooms nonstop loaded with flowers and im farther north the only problem i have is my pesty next door neighbors who hack them down to the ground considering a branch stuck out on "their side"