Anyone else seeing this?
Before anyone responds with "open a SR," I did back in November 2018. The SR is still open and has been assigned "Bug 29301463 - DENSE_RANK QUERY RETURNS INCOMPLETE RESULTS" with Severity 2.
It's 3 months and ticking. If any of you have an ODS/EDW reporting database on 12cR2 or greater, you may want to read further. If any of you think that a Statistical Analytic function that has been around since 10gR2 (or before?) might have some part to play for COST BASED OPTIMIZATION to work properly (I have no proof of such thing but I do wonder) might also want to read further.