I think ogvjs has become ES6 recently, but it isn't marked as es6 code ?
This causes errors on IE11
This likely happens for both the old and the new player, but as we have no client logging for IE11 it was hidden that this was throwing errors on IE11.
SCRIPT1002: Syntax error
ogv-support.js (1,4)
https://commons.wikimedia.org/w/extensions/TimedMediaHandler/resources/mwembed/lib/binPlayers/ogv.js/ogv-support.js?e4734