I have both a chromecast and a NP and only the NP exhibits this behavior...
When casting WatchESPN to my NP, whenever the program goes to commercial, the commercial audio track will become very slow. The video track is unaffected. The audio track remains slow for the remainder of the commercial, but then at the next commercial (or at the start of regular programming) the audio will return to normal. However, when it returns to normal the audio does not jump ahead to the match the live video feed, it continues to play from where it was on the track. Because of this, the audio feed trails the video for 30 seconds or more. It never catches back up. The only solution is to stop casting and cast again. This fix will work until the next commercial, where it happens again.
When casting WatchESPN to my NP, whenever the program goes to commercial, the commercial audio track will become very slow. The video track is unaffected. The audio track remains slow for the remainder of the commercial, but then at the next commercial (or at the start of regular programming) the audio will return to normal. However, when it returns to normal the audio does not jump ahead to the match the live video feed, it continues to play from where it was on the track. Because of this, the audio feed trails the video for 30 seconds or more. It never catches back up. The only solution is to stop casting and cast again. This fix will work until the next commercial, where it happens again.