The bug

The minimumVolume argument of /playsound is intended to provide a lower bound on the fade-out of sounds with distance, but instead it has no impact on the volume.

How to reproduce

1. Run this command:

   /playsound random.fizz @a 10000 0 10000 1 1
   

1. Since it's being played at distant coordinates, you can't hear it. This is intended.
2. Run this command:

   /playsound random.fizz @a 10000 0 10000 1 1 1
   

1. Notice the single change is the inclusion of the minimumVolume argument. It's set to 1, so the sound should be fully audible despite the sound being distant.
   →  It still can't be heard.
2. If desired, change the 10000 0 10000 to ~ ~ ~ to observe that the sound itself works perfectly fine, the problem is with minimumVolume doing nothing.