Check the distribution of your sampling points.
step 1: Change the code below to validate your primitives
var chl = ee.FeatureCollection("users/servirmekong/Vietnam/CHL_Boundary").geometry();
var plantations = ee.Image("users/servirmekong/Vietnam/primitives/plantations").rename('plantations')
var forest = ee.Image("users/servirmekong/Vietnam/primitives/forest").rename('forest')
var cropland = ee.Image("users/servirmekong/Vietnam/primitives/cropland").rename('cropland')
var urban = ee.Image("users/servirmekong/Vietnam/primitives/urban").rename('settlement')
var water = ee.Image("users/servirmekong/Vietnam/primitives/water").rename('water')
var plantations = ee.Image("users/servirmekong/Vietnam/primitives/plantations").rename('plantations');
var forest = ee.Image("users/servirmekong/Vietnam/primitives/forest").rename('forest');
var cropland = ee.Image("users/servirmekong/Vietnam/primitives/cropland").rename('cropland');
var urban = ee.Image("users/servirmekong/Vietnam/primitives/urban").rename('settlement');
var water = ee.Image("users/servirmekong/Vietnam/primitives/water").rename('water');
// Pre-define some customization options.
var options = {
title: 'histogram',
fontSize: 12,
hAxis: {title: 'probability (%)'},
vAxis: {title: 'count'},
};
// add the reference data
var referenceData = ee.FeatureCollection("users/servirmekong/Vietnam/ReferenceDataForestTraining");
// filter reference data
var waterPoints = referenceData.filter(ee.Filter.eq("land_type","water"));
var cropPoints = referenceData.filter(ee.Filter.eq("land_type","crop"));
var urbanPoints = referenceData.filter(ee.Filter.eq("land_type","urban"));
var plantationsPoints = referenceData.filter(ee.Filter.eq("land_type","plantations"));
var forestPoints = referenceData.filter(ee.Filter.eq("land_type","forest"));
var otherPoints = referenceData.filter(ee.Filter.neq("land_type","water"));
print(ui.Chart.image.histogram(water, waterPoints).setOptions(options))
print(ui.Chart.image.histogram(water, otherPoints).setOptions(options))
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