You may be missing a development configuration for your application.
In your angular.json navigate to architect -> build -> configurations and add these lines, below the definition of the production build:
"configurations": {
"production": {
// already there!
},
"development": { // this is new!
"buildOptimizer": false,
"optimization": false,
"vendorChunk": true,
"extractLicenses": false,
"sourceMap": true,
"namedChunks": true
}
},
"defaultConfiguration": "production"
And to run the build in development mode just type the next command: ng build --configuration development.