Dear Nhu,
For your question "user doesn't see all items", we may consider if it is caused by "filter" on the current view. To have further trouble shooting, we suggest you follow below steps to check it.
check any "filter" on the view.
- please go to the list >> list settings.
Scroll down under the views to see any views created.
Under the views contain all the views that were created on the site. Please check any views listed here. If so, please click on it to edit modify or delete.
2, create a new view in this way.
Could you please try to create new view please go to the list >> list settings click settings icon on upper top conner>> scroll down under views>>crate a view
For more information about filters and view please consider reading article
If the suggestion above doesn't work, given this situation, we do understand the inconvenience caused and apologize for it. Since you mentioned only this specific user has this problem, this issue may be related to specific account. We’d suggest you contact your office 365 administrator to go to Office 365 Admin Center-> Support-> New Service Request, the support engineers there have the correct escalation channel and this is the most efficient way to report such issue. You can refer to this article to check the way how to raise a ticket. Ways to contact support for business products - Admin help. The engineers in related team have higher permission and resources than us and they may help check it from background.
Thank you very much and have a nice day!