why did you have humidity? Dubias should not have humidity, it should be dry.
it should be warm, ~80-85F and a screen top with no moisture built up inside. I use an all plastic tub with screen hot glued onto the lid. there should not be little drops of humidity inside the setup
make sure your heat tape does not run under your water gel or it will evaporate it
They died because you didn't find proper husbandry for them before you started