UPDATE: After a great deal of time and sending SM large amounts of evidence and information the problem with missing items in my P7 downloads library has been solved (but not fixed).

SM:"This has been discovered to be an issue with the Cache in the new Library on MACs that prevents the some items from displaying when a Runtime has a large number of folders and will be fixed in the Service Release."

SM inform me that they working on the problem over the weekend, and a Service Release is imminent.

In the meantime using the search option remains the only way to use external runtime content if you have missing items.