LEDs often emit more blue spectrum light than older technologies, which makes them more effective at stopping melatonin production. See: https://en.wikipedia.org/wiki/Intrinsically_photosensitive_r...

LEDs also switch much faster than older lights, which means people can pulse-width modulate them, causing annoying flicker for people who're sensitive to it.

Admittedly both these problems are avoidable, but in practice they're seen as LED problems because they're so common with LEDs.