iPhone12/AppleWatch/AirPods/WorkoutApp/AudiobookApp Issue

Using an Apple Watch (Series 6), Apple AirPods Pro, and an iPhone 12, I walk using the Workout App with the playback of an mp3 using Audiobooks. During the walk, the Workout app generates various audio notifications, such as Ring Closed, or the number of minutes per mile. However, the behavior of these audio notifications happens in one of three ways: 1) I hear the Workout App audio notification coming from the watch itself; 2) the Audiobook App pauses, I hear the Workout App audio notification from my AirPods, but then I hear nothing and I have to manually restart the Audiobook App playback; and 3) the Audiobook App pauses, I hear the Workout App audio notification from my AirPods, then when the notification ends, the Audiobook App continues. Obviously, (3) is what I want. But what I get from day to day is sometimes (1), sometimes (2), and sometimes (3), in no particular order or pattern that I can discern. I do nothing in the way of changing settings to the phone or the apps between these three behaviors.

So, given that this is all Apple hardware and software that is supposed to work seamlessly together, for god’s sake, can someone please explain to me what is happening and why? In particular, can someone please explain how I can always get behavior (3)?

Thanks for your help!