I previously had this issue. It only affects admins who have the rights to change the order of the pinned topics which is why it's unlikely others can't reproduce on the OPs site.
However since 1.7 (could be Chrome 64) I no longer have the problem.
@zenkamal @a_5mith This sounds like it's due the new way we store post bookmarks.
Before, we stored the pid (e.g. 2341)
Now, we store the post index (e.g. 5)
The bookmark only updates if the current post # is > than the bookmarked post #
Unfortunately, 5 will never be greater than 2341, so the bookmark never goes away.
The old bookmark is basically trying to load the 2341th post in the topic, which doesn't exist. You can clear the bookmark by clicking the "x" at the top right of the notification alert, then that topic should be fixed.