Complex sentence: Because the intermediate carbocation, R +, is planar, the central carbon is not a stereocenter, even if it was a stereocenter in the original reactant, so the original configuration at that atom is lost.
Split into simpler sentences: Because the intermediate carbocation is planar, the central carbon is "not" a stereocenter. Even if it were a stereocenter prior to becoming a carbocation, the original configuration at that atom is lost.