So I'm not sure this is a bug but I wanna post this anyway because it is, it can screw the player pretty much over.
So I needed to face Zetta the first time. I lost against him and the game jumped me back to the Gearen Laboratory even though I used the healing point(s) a dozen of times at the Goldenwood Forest (and at the picnic place). I found that weird so I refrained myself from saving the game and went back to the Goldenwood Forest. There were no signs of Team Xen or Zetta or even Melia. And I pretty much searched through every possible place I could reach.
Obligatory question though I suspect the answer: is this intended?
I did not dare to investigate more mainly because quick saving is an automatic response of mine in this game (and Reborn), and I was afraid I was gonna save the game and possibly stuck in the game forever. So I did a soft-reset and beat Zetta...
But I suspect this is not how the game is intended, and you are actually unable to continue the plot whatsoever.