When Zombie Pigmen spawn from Nether portals, will immediately teleport back to the Nether

I'm using the 23x23x3 nether portal farm (3 23x23 nether portals adjacent, with all three lit/active). It appears pigmen are spawning in a portal, already touching one of the adjacent portals and is immediately teleported to the nether. I also was able to capture what is possibly happening in the attached video (go to 2:20). image-2020-04-26-23-27-13-498.png shows the pigmen who were teleported on to the other side in the attached video.