Did you find a resolution for this issue? If the issue still persists, please review the online help related to permissions and groups for Tableau Online.
If you are unable to resolve the permission issue once this has been reviewed, please share pictures/information about the user group setup and permissions. I'm guessing this user is not in the correct group within Tableau Online but a check online should tell.
I hope this helps.
On those other worksheets, are there any other filters that may be in conflict with the User filter? Maybe an artifact from testing or something?
Sorry about not updating this post. I have contacted Tableau tech support and they are working on this issue.
thanks for the update Ryan. If there is anything that can be shared as a learned experience for others, please come back and post.
Have a great weekend.