When a remote user in VRChat client navigates to my profile and presses View Avatar Details while I am wearing a private avatar, they cannot see the Acknowledgements section on that avatar. However, I can see them locally in "My Current Avatar", "My Avatars" avatar details, and on the website. This also happens in reverse, where I cannot see my friend's private avatar's Acknowledgements section.
This seems to only affect private avatars. The acknowledgements section of public avatars can be viewed (albeit Acknowledgements section in avatar details of public avatars are not viewable randomly).
This is a bug, because often avatar creators need to include and display acknowledgements / attribution for license compliance while in the same world instance.
A sample avatar IDs uploaded by me, with acknowledgements sections (private):
avtr_8a33bffc-c9dd-45a5-a18e-55a18a31c0ef
.
The screenshots attached show what a remote user sees about my avatar and what I see about my avatar in the avatar details.