I haven't used the ODBC connector (yet), but I have used the ExecuteSQL function in FileMaker (and they are very similar).
I noticed that all of your project numbers appear to contain only numbers and "legal" math operators. Is it possible that FileMaker is treating this field as numeric instead of text?
For example, the last project number: 12-02152/001 would become 2140 if it was treated as a numeric (computed) value.
I can certainly see why that would cause there to be non-unique values, but the MSSQL field type is nvarchar, does filemaker care about this? Does filemaker require a unique-key to be numeric?
According to your screen shot above, it looks like FileMaker is expecting a date field, and you say that MSSQL is treating it as a varchar field, so those should match.
Have you checked the field definitions and character type settings in your ODBC connector to make sure they are correct?
Issue was that the view I was using was grabbing data from a different table, and the ODBC user did not have permissions on the table.
Silly me... *facepalm*.