Several years ago, developers of music players on Android had to implement a persistent notification in order to keep their app running and music playing even when users switched to another app. With better memory management and more available RAM on modern phones, this isn't a concern anymore, and most devs have forgotten about that commodity. That has had one annoying consequence on several audio apps: If you mistakenly swipe them away, your music or podcasts or audiobooks stop playing.
Take the example of Google Play Music and YouTube Music, both apps developed by Google. In the former, if music is playing and you swipe the app away from Recents (aka Overview aka app switcher), nothing changes. Music continues normally, the notification stays, and you can simply tap it to get back to the app. YouTube Music behaves differently. After you swipe it away, music instantly stops but the notification sticks for a couple of seconds then disappears. You have to open the app again from the launcher and you can clearly see it's been paused.
Left: Google Play Music keeps going. Right: YouTube Music sticks for a few seconds then disappears.
This difference in behavior is also found in third-party audio apps. Pocket Casts, for example, doesn't stop your podcasts and keeps its notification on. The same is true for SoundCloud and TuneIn. Spotify and DI.FM, on the other hand, stop instantly when swiped away. It's certainly frustrating when you're jamming to a nice tune or in the middle of a sentence in a podcasts or book.
Left: Pocket Casts keeps the podcast going. Right: Spotify just closes entirely.
Not everyone will agree with me. However, this difference in behavior isn't just a personal preference, it's also a result of Android not clearly defining what the Recents/Overview screen is supposed to be. If you think of it as an app switcher, then it shouldn't matter whether an app is in it or not for it to be active, i.e. things can be happening in the background or through a notification, and dismissing the app shouldn't fully close it. If, however, you strictly consider it a task manager, then swiping away should close that app and thus stop all ongoing activities stemming from it.
Android allows developers to choose their own strategy for that screen, and that's not only true for audio players: Many apps don't close or stop all their activities when dismissed. For example, Chrome, YouTube, Google Drive, and the Play Store keep their ongoing downloads — obviously, no one would want them to stop unexpectedly.
For me (and many others) audio playback should be treated similarly; I don't want it to stop abruptly if I mistakenly swipe the app away. Even more confusing is the inconsistency: Each music or podcast app has decided to choose one way or the other, including Google's first-party Play Music and YouTube Music, leaving me to question what will happen after my swipe-happy finger triggers that gesture.
Implementing a sticky notification when music is playing doesn't seem to be a daunting task — Cody tells me it should be a 15 or 30-minute affair — so the solution is right there for every developer to use. Unfortunately, not all of them will, starting with Google's own teams.