3 year old own root climibig rose not doing well
I live in zone 5 and in the spring of 2020 I planted an own root climbing rose from Jackson&Perkins called Iceberg. It is located in the southeast corner of our house, close to the house itself (benefits from the heat in the winter, but it also gets its roots covered with straw to protect it from the cold) and has achieved some significant size (it is probably about 8 feet tall and rather bushy). However, since last year the rose has not been doing well. About 1/3 of its canes never developed leaves. Instead, the rose started growing branches from below. I am noticing that now the rose is similarly growing at the bottom; no sign of life on the canes. None of them is green, which makes me think that they may be dead. How could this happen given that this is not a grafted rose? I've cared for it to the best of my abilities--it is on a good watering schedule in the summer, I feed it and remove dead and infected leaves. I was told in the local greenhouse that the plant must be stressed as it grows new branches from below. Any idea what might be wrong? Is the plant salvageable?
PS There is another rose--an own root David Austin climber--just on the corner from the Iceberg, and that one is doing really well. I guess, I am trying to say that they grow in pretty much the same conditions. And yet...