I have just spotted that with the Pheromones bonus active helmets are being generated too fast: tt appears that the bonus is causing not only enemies to spawn faster.

During the last event there was one occasion that my token count was reading over 2500, but when attempting to start a new event objective I received an error… after reloading the count had been under 2500. I didn't report it back then because I couldn't identify a reason for it happening, I feel I've probably found the reason now.

Hope that helps! :)