Issues have not returned, marking this resolved. I'll follow up with an explanation from the ad serving provider.

Starting at 8 am ET, we became aware of an issue with responses for ad placements. The ad serving system's performance degraded from .15 to 1.5 secs per response. It has since recovered. Looking back, it appears this issue started shortly after 7 am, but only degraded to the point of causing issues ~8:10 am. The ad serving system recovered at 8:40, and audio and ad serving is now operating normally. We'll continue to monitor this issue and follow up what caused the ad serving issue.