Running

I'm seeing weird results with my heart rate strap. My ground contact time is really low, but my vertical oscillation is really high! One indicates good form, the other indicates bad form. My subjective experience is that my vertical oscillation is low, but my garmin disagrees.

And I think the reason why is the movement of my breasts. I think they're moving the sensor itself, and confusing its measurements.

Is that actually a thing? I've tried to find research or people talking about it, but all I can find is discussion on the impact of breasts on actual running performance, rather than on the measurement of it.