With no resource pack, sounds get quieter as the player gets further away from them, just as expected. When the player gets too far away, they will no longer be able to hear the sound at all. However, when a resource pack is applied, any sounds from the pack will not change in volume and instead remain at the maximum volume until the player gets too far away to hear the sound at all, at which point the sound will stop playing entirely.

I have created a video here to demonstrate the bug. The video was recorded in Minecraft 1.14.3, but I have tested and confirmed that this bug is still an issue in Minecraft 1.14.4 Pre-Release 5. I have also performed this test in 1.12.2 to make sure that this is in fact a bug and not intended behavior, and in 1.12.2, sounds from resource packs do get quieter as the player gets further away. It is unclear when this bug originated, but it has been around since at least 1.14.3.