Reddit users thevincentasteroid and MMD3_ posted about an auto-playing video ad (with sound) on the home screen. The ad is for Chicken Tender Wraps from Carl’s Jr. When it begins auto-playing, it pushes all the other UI elements out of focus and goes almost full-screen, returning to the home screen after it has played through once.
When you say it always has worked this way what is your frame of reference regarding time? I haven’t owned a chromecast in about 6 years. However prior to that chromecast had no ads whatsoever so the idea that there are ads at all is shocking to me. It certainly hasn’t always been this way. (I currently use an Apple TV)