Hi There,
Had a further look into this one as also managed to replicate in chrome!!
The fix seems to be making it so the movie start time is not 0 seconds. For me setting it to 1 second enabled the movie to play with browser in full screen mode.
Here is the gitlab project with the demo to download https://gitlab.pavlovia.org/lpxrh6/multiplemovie.
I hope this solves your problem!
Becca