Can't transform into Zenith in Infernal Base

[Barney Brown]

I beat Zenith and collected his DNA but when I talk to Mew my only transformation option is the Darkrai Cultist with Seed Flare and Tesseract underneath it (I’ve included an image). I quicksaved before the battle and tried running through it again and the same thing happened. I’m completely stumped and can’t think of anything to do other than just starting another file from the beginning, which will be a little annoying after playing for a little over 40 hours. Any help would be greatly appreciated, thanks.