I don't think I have an answer but hopefully these resources might be of some help:
1.) Vote up the request to have a native FileMaker connector so that our dev team can see the demand and prioritize accordingly:
2.) All other FileMaker ODBC issues in the community forum seem to indicate FileMaker doesn't like the default SQL in the ODBC driver. Others have resolved this by creating/utilizing a TDC file as detailed here: Customizing and Tuning ODBC Connections | Tableau Software
This idea came from this forum thread:Filemaker Data Issue
If by some lucky chance this answers/resolves your issue, please mark this response as 'correct' or 'helpful' so others can find it quickly.
Tableau Online Deployment Advisor