MSSQL NULL's Between specific dates
Move the condition from WHERE to JOIN:

FROM Object3 Object1 WITH(NOLOCK)
FULL OUTER JOIN Object4 Object5 WITH(NOLOCK) ON Object1.Column7 = Object5.Column8
FULL OUTER JOIN Object6 Object2 WITH(NOLOCK) ON Object5.Column9 = Object2.Column10
                                            AND Object2.Column11 &gt;= DATEADD(month, -1, @startOfCurrentMonth) 
                                            AND Object2.Column11 &lt; @startOfCurrentMonth