Audio not playing on Mac, Safari version 12.0.3

Hey Folks. I'm pulling my hair out on this one.  I am using the latest version of Storyline 360 3.49.24347.0

my QA person is on a Mac Mohave with Safari 12.0.2

She will be working along fine on a course and out of the blue, a slide's audio won't play. she'll hit the rewind button and it will play. we have about 6 courses on the go and she keeps reporting this problem in review.  I finally resurrected my mac with the same setup and sure enough. certain slides won't play audio the first time through. I'll go to the previous slide and then back and it plays perfectly.  Normally I would say don't use Safari but because of Covid and people working from home, we can't control what people are using.  I have spent probably 2 days trying to troubleshoot this and there doesn't seem to be any rhyme or reason why one slide won't work. then another one doesn't. I moved the audio file a smidge to the right on the offending slide and it seemed to work, then the next slide which worked before now doesn't work.  It almost feels like a buffering issue.  HELP!