A single user is not able to see all posts/pages from a topic. For example, we have a topic with 54 posts distributed to 6 pages. So every user sees "54 posts " while this user only sees "17 posts ". The 2 pages he sees contain only the newest posts.
The user tried it from different devices. He sees everything when not logged in, but as soon as he logs in, he only sees the subset of the posts. I checked the user-rights (which seems normal) as well as the user cleared all cookies and I cleared the forum-cache - without any changes.
Any ideas where to look?