@AlyssaK - the reason for this appears to be that AGLC4 says that subsequent references for secondary sources by default do not include the title (or short title), unless another work by the same author has already been cited. This is one of those rules that is difficult (and possibly impossible) to implement technically, because Zotero can recognise subsequent citations of the same item, but I don't think it can recognise that there has been a previously cited item by the same author previously. This is an example of what I would call an unnecessarily complex rule (which also makes more work for authors and editors).

You can flip the process so that your document includes the short titles by default, and then when you break the link at the end you can delete the short titles. Whether this works better for you depends on how many times you cite an author with multiple works, but I tend to find it easier to delete the short titles rather than go back and find them (and it also reduces the risk that you've accidentally cited the wrong work without realising it!)

I suspect @ljmoore221 that the issue is not with Zotero, but with your style. It may be a similar issue - journals come up with all kinds of crazy rules about short titles that make them difficult to implement!