The word soufflé is the past participle of the French verb souffler which means "to blow up" or more loosely "puff up" (thank you Wikipedia) - I never knew this but it makes sense...
- milk chocolate took the place of bittersweet chocolate,
- egg yolks were added after about 1/2 the whites were folded in (why were they across the kitchen near the coffee maker?!) and could have caused some over-mixing,
- maybe the rim wasn't clean and they "got stuck",
- powder sugar was added before baking.