You need to have unique names for every item in the group (e.g. Actual1 and Actual2). If they are the same name, they overlap instead of stack.
If you still have issues, you can copy/paste you chart into the thread and we can take a closer look. 
[
{
"type": "kyvislabs.display.apexchart",
"version": 0,
"props": {
"type": "bar",
"options": {
"chart": {
"dropShadow": {
"blur": 10,
"color": "#000",
"enabled": true,
"left": 7,
"opacity": 0.2,
"top": 18
},
"height": 350,
"toolbar": {
"show": false
},
"type": "line",
"events": {
"animationEnd": false,
"beforeMount": false,
"mounted": false,
"updated": false,
"mouseMove": false,
"mouseLeave": false,
"click": false,
"legendClick": false,
"markerClick": false,
"xAxisLabelClick": false,
"selection": false,
"dataPointSelection": false,
"dataPointMouseEnter": false,
"dataPointMouseLeave": false,
"beforeZoom": false,
"beforeResetZoom": false,
"zoomed": false,
"scrolled": false,
"brushScrolled": false
},
"stacked": true
},
"colors": [
"#0000FF",
"#00FF00",
"#FF0000"
],
"dataLabels": {
"enabled": true
},
"grid": {
"borderColor": "#e7e7e7",
"row": {
"colors": [
"#f3f3f3",
"transparent"
],
"opacity": 0.5
}
},
"legend": {
"floating": true,
"horizontalAlign": "right",
"offsetX": -5,
"offsetY": -25,
"position": "top"
},
"markers": {
"size": 1
},
"stroke": {
"width": 1,
"colors": [
"#fff"
]
},
"title": {
"align": "left",
"text": "Average High & Low Temperature"
},
"xaxis": {
"categories": [
"Jan",
"Feb",
"Mar",
"Apr",
"May",
"Jun",
"Jul"
],
"title": {
"text": "Month"
}
},
"yaxis": {
"max": 100000,
"min": 5,
"title": {
"text": "Temperature"
}
}
},
"series": [
{
"name": "Target",
"group": "target",
"data": [
44000,
55000,
41000,
67000,
22000
]
},
{
"name": "Actual",
"group": "actual",
"data": [
48000,
50000,
40000,
65000,
25000
]
},
{
"name": "Actual2",
"group": "actual",
"data": [
20000,
40000,
25000,
10000,
12000
]
}
]
},
"meta": {
"name": "apexchart"
},
"position": {
"x": 8,
"y": 165,
"width": 757,
"height": 499
},
"custom": {}
}
]