A short story for you that might or might not help...
When we bought our house, it had been empty for a few years. Bees had made a huge hive in one wall, and were coming in through a hole in the brick. I planted goldenrod and other plants for the bees right by the wall. A few years pass, we remodel, and put a door in that wall. A beekeeper moved the hive to a hive box down by our pond. (He said it was the biggest hive he had ever seen!)
I tried to dig out the plants that were now in front of the door, and thought I had most out. The goldenrod came back, though. I let it grow for 2 seasons, then decided it needed to go. I tried cutting it back, but that only encouraged it! Then one hot day, a hose was left running in that bed, flooding it. The goldenrod developed the moldy look yours has in the first photo. A few weeks late, i found the roots were soft and I was able to dig it out. sorry, I know yours is really nice looking and is properly sited. Mine was in heavy clay that did not drain well. Strangely enough, mine was on the north side of the house where snow and ice accumulate, and that didn't seem to affect it. Sogginess in heat did.
Is there something that has changed in your area where water might not be draining the way it should?
As far as I know, that's the only thing that hurts it.
