Steps to reproduce:

1.) Add at least 4 pages under website.
2.) Activate them taking note of the order they have been activated in.
3.) Check they all appear in the same order in the Inbox.
4.) Move the system (server) date less than 7 days ahead.
5.) Check all the workitems are still in the Inbox.
6.) Move the date 7 days or more ahead.
7.) Check the Inbox. Some of the items have disappeared.

In step 2, the order is of importance because most of the times the issue is reproduced the following observation is made:
If you number the items 1 to N being according the order they are activated into , after 7 days or more all items with odd numbers disappear and the ones with even numbers remain in the inbox.

When time is set back in testing items don't appear again.