What is this piece of plastic inside the sole?

That's very odd. What make are they? Like you said obviously by design, given the cut out but why on one side only? Could it be replaced by or actually be a footpod thing that would pair with a device to read cadence?

Semi-coincidentally I've been injured for over a month now having knackered my heel as a result of a hard lump of mis-set foam in one of my running shoes. First time I ever came across anything like it.