Since 17w15a custom resource pack sounds (not just changing vanilla sounds, the ones you have added and included in the sounds.json file) do not play a sound when /playsound(ed). This used to work fine in previous versions.
- Download the attached resource pack 17w15a Sound Bug.zip and load it
- Use the following command to try playing a custom sound
→ The sound is not played; additionally an error message appears in the log indicating that the sound could not be played
Note: The provided resource pack modifies the nether quartz ore texture as well, therefore you can check if the resource pack was loaded correctly by looking at a nether quartz ore block.