The original release for the snapshot 20w49a json was:https://launchermeta.mojang.com/v1/packages/ef769cdc1302b41eddfa04a0e8d96f6c16648020/20w49a.json

Points to assets index: 
https://launchermeta.mojang.com/v1/packages/e022240e3d70866f41dd88a3b342cf842a7b31bd/1.17.json

It was modified after the next snapshot or two happened to: https://launchermeta.mojang.com/v1/packages/13ef29a79cc0512e124963fd964e44fd11efe369/20w49a.json

Points to asset Index:
https://launchermeta.mojang.com/v1/packages/ecd216d8188230180af4163ee4f4901e28acee29/1.17.json

What was modified was the assets index url. I have seen some sounds change from this or another snapshot of the chest. 

Conclusion: your web json api gets modified or regenerated after each snapshot when it shouldn't modify older snapshot jsons. This is a bug what if you had totally different sounds/textures it would be noticeable by everyone playing that snapshot.