One out of several audio files on SL slide does not play

Hi all,

I have encountered a weird issue and don't know how to solve it. I have several audio parts on one slide, and apart from one they all play fine. I have aligned them, so there's no overlays and aligned animations to go with it.
This one particular audio was recorded in Storyline directly, like all the other ones. Preview of the audio works fine (plays well) but when I go into edit you can see no audio waves. When previewing the slide, all audio plays well apart from this one. 

I have already re-recorded the audio and aligned again to match the slides animation/other audio but it is still not playing in preview (and showing no audio waves in editing mode). How can I resolve this without having to redo the whole slide?

I have no active sound triggers in the slide, and nothing is locked or hidden in the timeline.

I am using Version  v3.83.314440.

If screenshots/more info is required please let me know.

Thanks.