I discovered two avatar audio bugs in worlds from Udon that have a gimmick for changing the player's avatar audio.

Executing SetAvatarAudioCustomCurve(false) makes the avatar audio for 3D settings for the local player extremely quiet.

3D settings mean that Enable Spatialization is checked for VRCSpatialAudioSource. This occurs regardless of the state of Use Audio Source Volume Curve.

Executing SetAvatarAudioCustomCurve(false) for a remote player does not seem to affect the volume.

Executing SetAvatarAudioCustomCurve(true) did not affect the volume for the local player, either.

Executing SetAvatarAudioForceSpatial(true) makes 2D avatar audio noisy, regardless of whether the player is local or remote.

2D settings mean that Enable Spatialization of VRCSpatialAudioSource is unchecked and Spatial Blend of AudioSource is set to 0 (2D side).