Storyline Course Freezing in Chrome, Edge and IE but not Firefox?

Hello. My apologies in advance for posting yet another discussion on course "freezing" since there are so many other threads on this general topic already - but I haven't found any (yet) that match our situation exactly. 

We have a Storyline course that some learners are now reporting "freezes" or "locks" up around the end of some slides. It appears some of these situations (if not most) are slides with audio playing as the slide animates/progresses. Some learners try to restart and re-"watch" the slide in hopes of being able to get to the next slide if they replay the entire slide but apparently this rarely works. 

This course has not had this kind of issue reported before as other learners have gone through it without an issue but this new group of learners is quite (naturally) frustrated and they are actually not allowed to use Firefox (this was only confirmed by their IT department).

FYI: Unfortunately I do not have very much detail on the course itself yet as I am not the developer/author but will share more detail on that later if/when I get it.

Does anyone have any articles or advice that could be of help here? Thank you in advance.