Using headphones - left channel bleeds into right (and vice-versa)

I am using headphones (1963 IEMs) and I have two distinct channels. Currently, the left side is completely muted, but it sounds like the right channel is bleeding into the “muted” left. It’s quiet, but loud enough that it sounds like crackling in my supposed-to-be-silent left ear. Same thing happens in the left ear when the right is muted.

I have no idea what’s going on, but I don’t like it. Anyone else experience this?

Edit 1: Instead of just muting, I changed one of the outputs to “not in use,” and nothing changed, still getting bleed from the other channel. I also tried to put a gain stomp into the signal gain and turn the volume all the way down… no dice

Edit 2: Took the headphones out and checked if this bleed over is happening with the other outputs… it is. It’s faint, sure, but I can clearly hear the left channel in the right speaker, even when the right channel is muted (and vice-versa)