The expression looks OK to me. First check the variable and the GetFieldSelections() function. Check the value of the variable and expression and and plug these values into the expression.
Should they have quotes?
Failing that, I would remove all the set filters and start with the basic expression:
=If(GetFieldSelections(OrdItemInsDt) > 0,
Sum(If(OrdItemDelDate <> OrdMasterOrdDate, OrdItemOrdKgs))/1000,
Sum(If(OrdItemDelDate <> OrdMasterOrdDate, OrdItemOrdKgs))/1000
Check the result and validate against your data model. Then add the set expression filters one at a time (except for the OrdItemInsDt, OrdItemInsDtWeek. If the result goes to zero, then you have no results matching all those conditions.