Same experience here in southern Ohio. Almost all the time the blossoms would ball or brown quickly. Probably too humid here. Rarely, one would have decent blooms if they were quickly cut. This one was shovel pruned.

I think your clues are "hot site", "difficult soil" and the fact many climbers require three years (or longer) to come into their own. Before you're going to get growth and flowers, they require roots under them. Hot, dry, difficult soil issue inhibit root formation. Few roots means few nutrients which can lead to malnourished plants. Under nourished and water stressed plants routinely suffer disease issues. It can be extreme enough to force otherwise bullet proof roses to become infected. I'd suggest doing whatever you can to alleviate the heat, dry and "bad soil" issues the rose is experiencing and then give it three years (at least, perhaps longer if the difficulties it experiences can't be fixed) to perform as expected.