It's an odd one that, I was never really able to track down the cause of it.
I've run some tests, hopefully it can help you :
Everything has been done using 7th heaven 2.0 and the mods directly included with itSo, for me the problem doesn't appear only whith the "Field Animation mod (Bloodshot + Kaldera)" activated, but also with "Field Models -Qhimm catalog -> ( Dynamic weapons -> Cloud -> 5 Ninostyle) OR -> ( Main caracters -> Cloud -> 6 - Ninostyle)", I tried other skin for Cloud (with "dynamic weapons" or "main caracter"), the one called "Bloodshot-classic", and without skin -> the bug doesn't appear.
So you CAN'T have ninostyle skin for CLOUD (Barret doesn't seems to be a problem, I tried it too), nor the Bloodshot + Kaldera mod activated.
And the bug always appear in the exact same moment :
1 - Barret say : "I dunno. ... the others ain't here either"
2 - Cloud rotate in order to face Barret
3 - Cloud say : "We went into the cave.. and then"
So the bug is appearing between 2 and 3 -> Cloud rotate to face Barret, but never start to talk.
Edit : Precised that I used 7th heaven 2.0 to get and manage the mods.