"Cannot find module" when trying to build app

まず、報告されている Ionic CLI、Node.js、npm のバージョンで ionic-app-scripts build --prod --target cordova --platform ios の失敗を再現します。webpack-sources/lib/Source.js と node_modules 配下にある欠落した source-map のパスを調査します。ionic repair を繰り返し使用せずにビルド、準備、実行が機能すれば完了です。

Description:
I have to run ionic repair now on a regular basis for being able to run, prepare or build my up.
This happens after using ionic cli a few times (usually i do runs, builds and prepares). Although i did not count: so i can't say if it happens always after the same count of usages.

Output:

> ionic-app-scripts build --prod --target cordova --platform ios
internal/modules/cjs/loader.js:236
      throw err;
      ^

Error: Cannot find module '/Users/jpf/Documents/projects/mobile-customer-app/node_modules/webpack-sources/node_modules/source-map/source-map.js'. Please verify that the package.json has a valid "main" entry
    at tryPackage (internal/modules/cjs/loader.js:228:19)
    at Function.Module._findPath (internal/modules/cjs/loader.js:365:18)
    at Function.Module._resolveFilename (internal/modules/cjs/loader.js:612:27)
    at Function.Module._load (internal/modules/cjs/loader.js:527:27)
    at Module.require (internal/modules/cjs/loader.js:683:19)
    at require (internal/modules/cjs/helpers.js:16:16)
    at Object.<anonymous> (/Users/jpf/Documents/projects/mobile-customer-app/node_modules/webpack-sources/lib/Source.js:7:18)
    at Module._compile (internal/modules/cjs/loader.js:776:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:787:10)
    at Module.load (internal/modules/cjs/loader.js:643:32) {
  code: 'MODULE_NOT_FOUND',
  path: '/Users/jpf/Documents/projects/mobile-customer-app/node_modules/webpack-sources/node_modules/source-map/package.json',
  requestPath: 'source-map'

Steps to Reproduce:
Just use the cli during the development process.

My ionic info:

Ionic:

   Ionic CLI          : 5.2.3 (/usr/local/lib/node_modules/ionic)
   Ionic Framework    : ionic-angular 3.9.8
   @ionic/app-scripts : 3.2.4

Cordova:

   Cordova CLI       : 9.0.0 (cordova-lib@9.0.1)
   Cordova Platforms : android 8.0.0, ios 4.5.5
   Cordova Plugins   : cordova-plugin-ionic-webview 1.2.1, (and 17 other plugins)

Utility:

   cordova-res : 0.6.0 
   native-run  : 0.2.8 

System:

   Android SDK Tools : 26.1.1 (/Users/jpf/Library/Android/sdk)
   ios-deploy        : 1.9.4
   NodeJS            : v12.6.0 (/usr/local/Cellar/node/12.6.0/bin/node)
   npm               : 6.9.0
   OS                : macOS Mojave
   Xcode             : Xcode 10.3 Build version 10G8