Just a thought: Is the game set for surround sound, and you're only capturing the front corners?
Normally, if OBS gets all 6 channels of 5.1 surround, it'll downmix all of that to stereo:
- The two left corners both go to the left channel
- The two right corners both go to the right channel
- The center channel goes to both
- The subwoofer disappears
In that case, you'll get everything.
(The sub is supposed to be redundant, and only used to relieve the load on the other 5, so the earthquakes and such can be mixed at a sensible level in them and still shake the room. Underpowered systems often remove bass from the other 5 and put that in the sub as well, so just listening to each speaker isn't necessarily a good indication of what was originally in each channel.)
Anyway, if OBS only gets the front corners, and the dialogue that you're missing is in the center, that could produce your examples here.