Hard to tell exactly what it could be. This is a stressful time to be planting shrubs in my neck of the woods for example. Temps hit the 90s in May and keep going up after that. Transplant shock is the first thing I think about in such a case. You may have kept the soil moist but with a smaller root system than it used to have, it may not have been able to support all the stuff growing above the ground. It probably was enough when it started blooming but once the heat showed up, it became too much and the shrub aborted the blooms early. See if it does better next year. I would either deadhead them when they turn brown or leave them "on" for winter interest.

Just wondering how far did the bloom get before browning out? Did the blooms stay white and turn brown? Or did they change from white to pink? Or did they change from white to pink to magenta?

It sounds like the plant got water on the blooms and then the sun hit it and scorched them.

VS blooms only last about a month...