Cant seem to build ionic app in --prod

Ionic Framework ionic-v3
1

I keep getting this error whenever I ionic build android --prod. it works fine with ionic serve and ionic run. even ionic build is okay.

Error: Cannot determine the module for class SupplierChequeModalPage in C:/wamp/www/pos/src/pages/supplier-cheque-modal/supplier-cheque
-modal.ts! Add SupplierChequeModalPage to the NgModule to fix it.
Cannot determine the module for class LetterAvatarDirective in C:/wamp/www/pos/src/directives/letter-avatar/letter-avatar.ts! Add Lette
rAvatarDirective to the NgModule to fix it.
Cannot determine the module for class ClientChequeModalPage in C:/wamp/www/pos/src/pages/client-cheque-modal/client-cheque-modal.ts! Ad
d ClientChequeModalPage to the NgModule to fix it.
Cannot determine the module for class CustomerModalPage in C:/wamp/www/pos/src/pages/customer-modal/customer-modal.ts! Add CustomerModa
lPage to the NgModule to fix it.
Cannot determine the module for class LowStockFilterPipe in C:/wamp/www/pos/src/pipes/low-stock-filter/low-stock-filter.ts! Add LowStoc
kFilterPipe to the NgModule to fix it.
Cannot determine the module for class DateFilterPipe in C:/wamp/www/pos/src/pipes/date-filter/date-filter.ts! Add DateFilterPipe to the
 NgModule to fix it.
    at Error (native)
    at syntaxError (C:\wamp\www\pos\node_modules\@angular\compiler\bundles\compiler.umd.js:1550:34)
    at analyzeAndValidateNgModules (C:\wamp\www\pos\node_modules\@angular\compiler\bundles\compiler.umd.js:22948:15)
    at AotCompiler.compileAll (C:\wamp\www\pos\node_modules\@angular\compiler\bundles\compiler.umd.js:22721:18)
    at CodeGenerator.codegen (C:\wamp\www\pos\node_modules\@angular\compiler-cli\src\codegen.js:30:14)
    at Function.NgTools_InternalApi_NG_2.codeGen (C:\wamp\www\pos\node_modules\@angular\compiler-cli\src\ngtools_api.js:61:30)
    at Object.doCodegen (C:\wamp\www\pos\node_modules\@ionic\app-scripts\dist\aot\codegen.js:6:51)
    at C:\wamp\www\pos\node_modules\@ionic\app-scripts\dist\aot\aot-compiler.js:42:30