I try crop classification for wheat crops in my study area. My code very well works for the 2016-2019 years. But for the 2020 year, my code did not work. I will appreciate if someone advises me Thank you! Here is my code:

var Polygon = 
    /* color: #d63000 */
    /* displayProperties: [
      {
        "type": "rectangle"
      }
    ] */
    ee.Geometry.Polygon(
        [[[9.671764962717377, 50.72618024130225],
          [9.671764962717377, 49.65178588495313],
          [11.182385079904877, 49.65178588495313],
          [11.182385079904877, 50.72618024130225]]], null, false);




//Import S2 image collection, // Define a cloud masking function and Selected Boundary // Selected period  
var collection4 = ee.ImageCollection('COPERNICUS/S2').filterMetadata('CLOUDY_PIXEL_PERCENTAGE', 'less_than', 20).filterBounds(Polygon).filterDate('2020-05-01', '2020-05-15');
var image4 = collection4.mean();


// Define an index function (selected NDVI value).
var ndvi4 = image4.normalizedDifference(['B8', 'B4']).gt(0.4);

//Import S2 image collection, // Define a cloud masking function and Selected Boundary // Selected period  
var collection5 = ee.ImageCollection('COPERNICUS/S2').filterMetadata('CLOUDY_PIXEL_PERCENTAGE', 'less_than', 20).filterBounds(Polygon).filterDate('2020-06-15', '2020-06-30');
var image5 = collection5.mean();

// Define an index function (selected NDVI value).
var ndvi5 = image5.normalizedDifference(['B8', 'B4']).lt(0.3);

//Import S2 image collection, // Define a cloud masking function and Selected Boundary // Selected period  
var collection6 = ee.ImageCollection('COPERNICUS/S2').filterMetadata('CLOUDY_PIXEL_PERCENTAGE', 'less_than', 20).filterBounds(Polygon).filterDate('2020-07-01', '2020-07-15');
var image6 = collection6.mean();

// Define an index function (selected NDVI value).
var ndvi6 = image6.normalizedDifference(['B8', 'B4']).lt(0.3);

//NDVI collection 
var wheat = (ndvi4).and(ndvi5).and(ndvi6)



var wheatViz = {min: 0, max: 1, palette: ['#FFFFFF00', 'blue']}
//var wheatMask = wheat.eq(1)
var ndviMasked = wheat.updateMask(wheat.gte(0.5))
Map.addLayer(ndviMasked.clip(Polygon), wheatViz, 'wheat')

I try crop classification for wheat crops in my study area. My code very well works for the 2016-2019 years. But for the 2020 year, my code did not work.

Here is my code:

var Polygon = 
    /* color: #d63000 */
    /* displayProperties: [
      {
        "type": "rectangle"
      }
    ] */
    ee.Geometry.Polygon(
        [[[9.671764962717377, 50.72618024130225],
          [9.671764962717377, 49.65178588495313],
          [11.182385079904877, 49.65178588495313],
          [11.182385079904877, 50.72618024130225]]], null, false);




//Import S2 image collection, // Define a cloud masking function and Selected Boundary // Selected period  
var collection4 = ee.ImageCollection('COPERNICUS/S2').filterMetadata('CLOUDY_PIXEL_PERCENTAGE', 'less_than', 20).filterBounds(Polygon).filterDate('2020-05-01', '2020-05-15');
var image4 = collection4.mean();


// Define an index function (selected NDVI value).
var ndvi4 = image4.normalizedDifference(['B8', 'B4']).gt(0.4);

//Import S2 image collection, // Define a cloud masking function and Selected Boundary // Selected period  
var collection5 = ee.ImageCollection('COPERNICUS/S2').filterMetadata('CLOUDY_PIXEL_PERCENTAGE', 'less_than', 20).filterBounds(Polygon).filterDate('2020-06-15', '2020-06-30');
var image5 = collection5.mean();

// Define an index function (selected NDVI value).
var ndvi5 = image5.normalizedDifference(['B8', 'B4']).lt(0.3);

//Import S2 image collection, // Define a cloud masking function and Selected Boundary // Selected period  
var collection6 = ee.ImageCollection('COPERNICUS/S2').filterMetadata('CLOUDY_PIXEL_PERCENTAGE', 'less_than', 20).filterBounds(Polygon).filterDate('2020-07-01', '2020-07-15');
var image6 = collection6.mean();

// Define an index function (selected NDVI value).
var ndvi6 = image6.normalizedDifference(['B8', 'B4']).lt(0.3);

//NDVI collection 
var wheat = (ndvi4).and(ndvi5).and(ndvi6)



var wheatViz = {min: 0, max: 1, palette: ['#FFFFFF00', 'blue']}
//var wheatMask = wheat.eq(1)
var ndviMasked = wheat.updateMask(wheat.gte(0.5))
Map.addLayer(ndviMasked.clip(Polygon), wheatViz, 'wheat')