I doubt it was the heat. I have two that have both put out new shoots and grown a foot over the summer when heat was 105 at times. Maybe they got too much sun or some passing animal gave them a rinse? I sure wouldn't give up on them...rather replant them in a shady spot.

mine has been doing great here in west texas, and it has been a hot summer here. The heat has done some damage to the leaves but it is growing very well.

I did have the same situation you are having first time I grew stuttgarts, I think a fungus got them.

I had the same problem two different times over the last few years with this one. With one of my trades however, a non-variegated portion was sent along with the variegated and while I lost the variegated stuttgart similar to above, the non-variegated has thrived for several years and blooms all summer in full sun. I think I 'm going to give it another try.