Cross references not creating links in ePub

When I create an ePub from a book with cross references (xref in the original Dita) they do not create links. The expected text appears and it is wrapped in an <a> tag, but it has no href attribute.

In the past few months I have created ePubs using essentially the same template/structapp/publish settings and the links appeared as expected. 

I went to one of those projects and republished it as ePub and now the links do not appear.  The only difference I can think of is that I recently updated my FrameMaker 2017 to the latest version (14.0.3.500).

Does anyone know if they made any changes to ePub publishing in recent updates?

Does anybody have an idea how I can fix my cross reference links?

Thanks for your help,

- Keith