Got the same bug at the same point; this time I watched as an ally destroyed the final enemy in the phase at which point all voicelines immediately stopped. In the first instance I was in the F. GR.-4 and the second time I was in the KF. 21.
Hey buddy, thanks for reporting. Is this in the Ogre/Grendel operation? I think I'm beginning to see a pattern which I can use to debug what causes the problem.