Videos Won't Play in Export

I downloaded the presentation with no problem, but both times I’ve done it (the earlier version of this year’s as well as the most recent download) there is no animation and no video. The only video that I can find that will play for me is “Did You Know”, in the Med Misc section.  Every other video goes to a blank with the control bar at the bottom, and won’t play.  I didn’t even realize that there was animation on the main pages of the presentation until someone shared their screen with me to show what it was supposed to be doing. 

That’s bad enough, but here is where it gets really weird.  Ever since I downloaded this last version of the pres on Friday, I can no longer play any videos in last year’s presentation, either.  I was going to use it yesterday for a virtual presentation, but none of the videos would play.  Do you have ANY idea what could be causing this issue?  Could I have deleted something important somehow (although I don’t remember deleting anything at all)?  The weird thing is that last year’s was playing fine all year and all summer, even after downloading the first version of this year’s presentation.  And my computer plays every other kind of video; Netflix, YouTube, etc., with no problem.  It’s just since the Friday that it’s affecting both.  I’m so confused as to what could be causing this. 

[We export the file in HTML5. The videos are all locally sourced.]