Duplicate main-es2015 file downloaded on page load

On refreshing an angular application. In the network tab on filter able to see main-es2015 being shown as downloaded:

EDIT: tsconfig.app.json

{
   "extends": "./tsconfig.json", 
   "compilerOptions": { "outDir": "./out-tsc/app", "types": [] },      
   "files": ["src/main.ts", 
   "src/polyfills.ts", 
   "src/typings.d.ts"],  
   "include": ["src/**/*.d.ts"], 
   "exclude": ["src/test.ts", "src/**/*.spec.ts", "*/.stories.*"] 
}