Sprinting off from the lights is a bit over-rated, you'll find you wear components out really fast. Especially on this fashion for compact chain sets.

It sounds like you're slowing for the lights, and then others are dropping you just as the lights change? So guessing here: the lights sequence to make a 'green wave'? Find out what that timing is, work the numbers to find average speeds, and try to stick to one you can manage. You'll then find you're doing the one doing the dropping.

Alternately, do a trick the slow ones do in Copenhagen: as the lights change wobble off all the way and back across the cycle path, it'll slow them down behind you, ruin their cadence, maybe cause a pile-up. You can then cycle off oblivious to the carnage behind you, and no one will overtake for a good while, and they'll do it slowly, if they catch up.