The problem with Allen’s meister ability is that calls upon more Kishin eggs. Becoming too strong to the point of losing control basically makes him a beacon for Kishin eggs. So it’s no wonder that the pair was quickly surrounded by them, to the point of almost being overwhelmed by the enemy.

Good thing they aren’t as bad as they were at first. And good thing that Kaworu has his A.T.Field, using it to keep the kishin eggs away as Allen fought with the Ooken. It’s during this that they find out the shield formed can move and shove the enemy away without requiring much energy from the pair.

The battle is difficult and being the beacon Allen is, the pair has to eventually retreat to safety – admittedly, kaworu sort of drags Allen away from it, because it eventually becomes too difficult (read: impossible) for Allen to keep going, not only because there are just too many kishins around both of them, but because he can’t possibly focus on his resonance with Kaworu properly.

(Boku is on hiatus, i hope it's alright if I'm the one posting this?)