RANKX not working

Okay... have spent a few hours in forumns reviewing a myriad of patterns for RankX.  Basic, advanced, using filters, AllSelected, ETC, ETC and still my table shows 1's for every line.  I have built similar tables and had zero issues with rankx.  The only thing different on this table is instead of fixed date ranges (i.e. last 12, last 6, etc.) these are actual MONTH Date fields for last 12 calendar months.  I have to believe this is a major factor in every row showing 1 as rank.  There will either be a date slicer or the visual will be "prefiltered" to the last 4 months in the final version.

What am I missing that is preventing this from working???

Any help, as usual, is always appreciated.

SMG