I think running into each other underwater might make the mos sense? Percy is having a Personal Issue that involves him trying to see if he'll drown like a dumbass, so he'll be floating around under the water. Maybe if Nita has grabbed Kara they can be swimming around and Noh-Varr can be chilling out underwater too and they kind of accidentally push through where the barrier used to be all wow I didn't know that could happen, let's explore!!