Reproduction steps(GIF attached):
1. Open the attached project.
2. Open the "Untitled" scene.
3. Double click "NewAudioMixer" and select Master channel.
4. Play the scene.
5. Click "Edit in Play Mode".
6. Slide the "Delay" bar to the far left and then to the far right in the inspector under the "Echo" sound effect.
7. Wait for 15 seconds.
8. Stop the scene.

Actual result:
Sound should be playing for 1-15 seconds.

Expected result:
Sound stops when the scene is stopped.

Reproduced with:
5.4.4p2, 5.6.0b5

Note:
Most likely a duplicate of 620018.