Hello team Minnekraft!
The /playsound for sounds out of minecraft does work just like in 15A and lower, but the custom sounds using sounds.json give the feedback that they are played but they aren't. Seems to me like something in the json has changed. This isn't directly a bug, but very bad for mapmakers if No One knows what has changed or if it's just a real bug
Have a nice day, Yobel
Environment
No matter in which world, using a resource-pack with the sounds.json to integrate custom sounds
Duplicate of MC-115810. Go and upvote that ticket instead. Also please use the search function next time.