Summary of issue: In the publication curation workflow the title of the citation does not appear. In fact the citation is essentially blank.
Summary of fix: The test for the presence of a citation key (such as title) was incorrectly returning false even though it was set. I changed asset($row->$key) to asset($row[$key]), which returns true when set. Apparently there was change in the way PHP handles this type class attribute reference.
Summary of testing: The issue was replicated on my dev machine and now works with this fix.