Thank you @raul_hijosa_nieto.
Issue has been identified a couple of hours after IMA released their fix and it has been patched across all hosted versions.
The issue began with after IMA released v3.205.0: https://developers.google.com/interactive-media-ads/docs/sdks/html5/v3/history
You analysis was correct, see fix here: https://github.com/kaltura/mwEmbed/commit/31138a55db362eaf7209c6e17629346fd74c59dd
If you are a user of the library, and are using it directly please use 2.69 which will be released next week.