For future readers, here is a correct implementation:
evalscript = """
//VERSION=3
var earliest_date = '2017-04-09'; var latest_date = '2017-04-30';
function setup() {
return {
input: [
{
bands: ["VV","VH","localIncidenceAngle","scatteringArea", "shadowMask","dataMask"],
}
],
output:[
{
id: "VV",
sampleType: "FLOAT32",
bands: 1
},
{
id: "VH",
sampleType: "FLOAT32",
bands: 1
},
{
id: "LocalIncidenceAngle",
sampleType: "UINT8",
bands: 1
},
{
id: "ScatteringArea",
sampleType: "UINT8",
bands: 1
},
{
id: "ShadowMask",
sampleType: "UINT8",
bands: 1
}
],
mosaicking : "ORBIT"
};
}
function updateOutput(outputs, collection) {
Object.values(outputs).forEach((output) => {
output.bands = collection.scenes.length;
});
}
function updateOutputMetadata(scenes, inputMetadata, outputMetadata) {
var dds = [];
for (i=0; i<scenes.length; i++){
dds.push(scenes[i].date)
}
outputMetadata.userData = { "acquisition_dates": JSON.stringify(dds) }
}
function preProcessScenes (collections) {
var allowedDates = [];
for(allowedDates,dt=new Date(earliest_date); dt<=new Date(latest_date); dt.setDate(dt.getDate()+12)){
allowedDates.push(new Date(dt).toISOString().split('T')[0]);
}
collections.scenes.orbits = collections.scenes.orbits.filter(function (orbit) {
var orbitDateFrom = orbit.dateFrom.split("T")[0];
return allowedDates.includes(orbitDateFrom);
})
return collections
}
function evaluatePixel(samples) {
var n_observations = samples.length;
let vv = new Array(n_observations).fill(NaN);
let vh = new Array(n_observations).fill(NaN);
let localIncidenceAngle = new Array(n_observations).fill(NaN);
let scatteringArea = new Array(n_observations).fill(NaN);
let shadowMask = new Array(n_observations).fill(NaN);
for(i=0; i<n_observations; i++){
var sample = samples[i];
if(sample.dataMask ==1){
vv[i] = sample.VV ;
vh[i] = sample.VH ;
localIncidenceAngle[i] = sample.localIncidenceAngle ;
scatteringArea[i] = sample.scatteringArea ;
shadowMask[i] = sample.shadowMask ;
}
}
return {
VV: vv,
VH: vh,
LocalIncidenceAngle: localIncidenceAngle,
ScatteringArea: scatteringArea,
ShadowMask: shadowMask
};
}
"""
bbox = BBox(bbox=[133.805, 48.201, 134.285, 48.391], crs=CRS.WGS84)
request = SentinelHubRequest(
evalscript=evalscript,
data_folder = "datasets",
input_data=[
SentinelHubRequest.input_data(
data_collection=DataCollection.SENTINEL1_IW,
time_interval=('2017-04-09', '2017-04-30'),
mosaicking_order="leastRecent",
other_args={"dataFilter": {"resolution": "HIGH"},"processing": {"backCoeff": "GAMMA0_TERRAIN","orthorectify": True,"demInstance": "COPERNICUS_30"}}
),
],
responses=[
SentinelHubRequest.output_response('VV', MimeType.TIFF),
SentinelHubRequest.output_response('VH', MimeType.TIFF),
SentinelHubRequest.output_response('LocalIncidenceAngle', MimeType.TIFF),
SentinelHubRequest.output_response('ScatteringArea', MimeType.TIFF),
SentinelHubRequest.output_response('ShadowMask', MimeType.TIFF),
SentinelHubRequest.output_response('userdata', MimeType.JSON)
],
bbox=bbox,
size=[512, 304.068],
config=config
)
I’ll try to add this script to the list of custom-scripts ASAP 
My last interrogation concerns this issue which was raised a couple of months ago here: Sentinel-1 Mosaicking order is always most recent, I’ll try to check on my side but if somebody from sentinel-hub can confirm whether the issue has been solved it would be great !