VEGA - area chart - strange data point behaviour - elasticsearch

Question

Does somebody know why my data points are twisted at some positions? (fig.1)
I use the same data-set in Vega-Lite and it works there. But in Vega I'm missing someting.
Maybe someone can help me out in this regard that would be most welcome :)
Datasample:
{
"score" : 18,
"time_out" : false
"hits" : {
"total" : {
"value" : 0123,
"relation" : "eq"
},
"max_score" : 1.8,
"hits" : [
{
"_index" : "dataIndex",
"_type" : "log",
"_source" :{
"#timestamp" : "2017-01-13345:00:16.0301135Z"
"numericValue" : 2.0
}
},
{
"_index" : "dataIndex",
"_type" : "log",
"_source" :{
"#timestamp" : "2017-02-20345:10:16.0301135Z"
"numericValue" : 3.0
}
}
]
}
}
Fig.1
Example in Vega - everything works as expected, except some points are skewed
{
$schema: https://vega.github.io/schema/vega/v5.json
data: [
{
name: table
url: {
%context%: true
%timefield%: #timestamp
index: dataIndex-*
body: {
size: 1000
aggs: {
hits: {
date_histogram: {
field: #timestamp
fixed_interval: 10m
extended_bounds: {
min: { %timefilter%: min}
max: { %timefilter%: max}
}
}
}
}
}
}
format: {
property: hits.hits
}
transform: [
{
type: formula
as: varTime
expr: toDate(datum._source['#timestamp'])
}
{
type: filter
expr: datum._source['#timestamp'] != null && datum._source['numericValue'] > 0
}
]
}
]
scales: [
{
name: xscale
type: time
range: width
domain: {
data: table
field: varTime
}
}
{
name: yscale
type: linear
range: height
domain: {
data: table
field: _source.numericValue
}
}
]
axes: [
{
orient: bottom
scale: xscale
format: %H:%M
}
{
orient: left
scale: yscale
}
]
marks: [
{
type: area
from: {
data: table
}
encode: {
enter: {
x: {
scale: xscale
field: varTime
}
y: {
scale: yscale
field: _source.numericValue
}
y2: {
scale: yscale
value: 0
}
fill: {
value: steelblue
}
}
update: {
fillOpacity: {
value: 1
}
}
hover: {
fillOpacity: {
value: 0.5
}
}
}
}
]
}

Answer 1

"sort": [ { "#timestamp": { "order": "desc" } } ]
...
in the body did the trick. The why still eludes me.