The reason for licensing issue is that the “oof” sound is not created by Roblox as its originally created by Tommy Tallarico, formerly a video game composer who made for the FPS Messiah, released in 2000
In 2020, when Tallarico first discovered Roblox’s use of the effect he came to an agreement with Roblox where anyone building a Roblox game experience would have to pay $1 (or 100 Robux) to be able to use the sound in their creation.