Apparently there’s a bug with audio scrubbing in LW 11.5 which causes distortion and echoing playback, making it impossible to do things like lip-syncing or audio-dependent motions.

So, in the meantime, I think I can manage if I animate all of the character’s facial expressions and jaw movement in Lightwave 9.6 and then transfer those motions to the 11.5 scene file. Kind of a pain in the ass, but it is all I can do until the bug gets fixed. I’ve submitted the issue to Newtek using the video shown above demonstrating the issue (the lighter colored interface is LW 9.6, darker is 11.5).