Interpolate function not working as expected

Hi All,
I have an infotable that has missing values (interpolate_1),
I use the following code (interpolate_params) to try and fill the gaps by the last element.

	var params = {
		mode: "INTERVAL" /* STRING */ ,
		timeColumn: "timestamp" /* STRING */ ,
		t: loggedValues /* INFOTABLE */ ,
		ignoreMissingData: false /* BOOLEAN */ ,
		stats: "LAST" /* STRING */ ,
		endDate: endDate /* DATETIME */ ,
		columns: "p1_plasma__cooling_water__conductivity__actual;p1_plasma__cooling_water__conductivity__limit_high" /* STRING */ ,
		count: 1000 /* NUMBER */ ,
		startDate: startDate /* DATETIME */
	};

	// result: INFOTABLE
	var interpolatedLogged = Resources["InfoTableFunctions"].Interpolate(params);

For some reason, the gaps are not filled, and the timestamp is not stretched correctly.
Please let me know what am I doing wrong ?

Thanks