@Spacehistory @Artemis201 That's an interesting problem. It might be some tightness; next time you're doing this and come to a stop, try some stretching out of that area for the duration to see if it helps.
Or, I suppose, consult a sports doctor. (I know, I know)
@Spacehistory Not an expert: maybe check how you slowdown. In sprinting, as an extreme instance, if one slows down too quickly it can result in hamstring strain.
Maybe as a run gets longer, you tend to over-stride a bit and marginally tire your hamstrings more & a sudden slow-down at a light causes soreness.
@Spacehistory Maybe consider paying for a stride assessment?
DIY possibilities: strengthen hamstrings & rear chain with deadlifts; check your starting stride as you leave the light, figure out which of your feet in your natural "pickup" foot for starts, learn how to do erect "fall" starts