We are working on a new angular ionic app and it builds on all our machines from powershell but on our build machine when it pulls the files from perforce to our D: drive it fails to build. Our build machine is using teamcity and we are using the powershell build step to run our ng commands. I can take the exact same files and they will build if I point the powershell script to them explicitly (I even deleted node_modules before doing this).
Here is the error we get. I removed the parts of the path’s related to our build machine to keep it cleaner.

ERROR in ./src/global.scss (<path to application>/node_modules/css-loader/dist/cjs.js??ref--13-1!<path to application>/node_modules/postcss-loader/src??embedded!/node_modules/sass-loader/dist/cjs.js??ref--13-3!./src/global.scss)
Module build failed (from <path to application>/node_modules/postcss-loader/src/index.js):
Error: Failed to find '@ionic/angular/css/core.css'
  in [
    <path to application>\projects\ta\src
   ]
   at resolveModule.catch.catch (<path to application>\node_modules\postcss-import\lib\resolve-id.js:35:13)
@ ./src/global.scss 2:26-225
@ multi ./src/theme/variables.scss ./src/global.scss ./src/theme/site.scss

I checked if the @ionic/angular/css/core.css file was really missing and it was in the node_modules even when it fails to find it.
We use the following command to build

ng run ta:build --verbose

We are using the following versions of various pieces of software

• Npm: 6.9.0
• Angular CLI: 1.6.7
• Node: 10.16.0

I am not very familiar with building angular apps so if there is other information you need from me give me the heads up and I can provide it.

{
   "name": "tenantapp",
   "version": "0.0.1",
   "author": "Ionic Framework",
   "homepage": "https://ionicframework.com/",
   "scripts": {
      "ng": "ng",
      "start": "ng serve",
      "build": "ng build",
      "test": "ng test",
      "lint": "ng lint",
      "e2e": "ng e2e",
      "start:ta": "node --max-old-space-size=8192 \"node_modules\\@angular\\cli\\bin\\ng\" serve ta --open",
      "build:ionic": "ionic build"
   },
   "private": true,
   "dependencies": {
      "@angular/animations": "^10.0.9",
      "@angular/cdk": "^10.1.3",
      "@angular/common": "~9.1.6",
      "@angular/core": "~9.1.6",
      "@angular/forms": "~9.1.6",
      "@angular/material": "^10.1.3",
      "@angular/platform-browser": "~9.1.6",
      "@angular/platform-browser-dynamic": "~9.1.6",
      "@angular/router": "~9.1.6",
      "@angular/service-worker": "~9.1.6",
      "@capacitor/android": "^2.3.0",
      "@capacitor/core": "2.3.0",
      "@capacitor/ios": "^2.3.0",
      "@ionic-native/core": "^5.0.7",
      "@ionic-native/splash-screen": "^5.0.0",
      "@ionic-native/status-bar": "^5.0.0",
      "@ionic/angular": "^5.0.0",
      "@ionic/cli": "^6.12.1",
      "@ionic/pwa-elements": "^3.0.1",
      "fibers": "^3.1.0",
      "ng-recaptcha": "^6.0.2",
      "node-sass": "^4.14.1",
      "primeng": "^10.0.0-rc.3",
      "rxjs": "^6.5.5",
      "tslib": "^1.10.0",
      "zone.js": "~0.10.2"
   },
   "devDependencies": {
      "@angular-devkit/build-angular": "~0.901.5",
      "@angular/cli": "~9.1.5",
      "@angular/compiler": "~9.1.6",
      "@angular/compiler-cli": "~9.1.6",
      "@angular/language-service": "~9.1.6",
      "@capacitor/cli": "2.3.0",
      "@ionic/angular-toolkit": "^2.1.1",
      "@types/jasmine": "~3.5.0",
      "@types/jasminewd2": "~2.0.3",
      "@types/node": "^12.11.1",
      "codelyzer": "^5.1.2",
      "jasmine-core": "~3.5.0",
      "jasmine-spec-reporter": "~4.2.1",
      "karma": "~5.0.0",
      "karma-chrome-launcher": "~3.1.0",
      "karma-coverage-istanbul-reporter": "~2.1.0",
      "karma-jasmine": "~3.0.1",
      "karma-jasmine-html-reporter": "^1.4.2",
      "protractor": "~5.4.3",
      "ts-node": "~8.3.0",
      "tslint": "~6.1.0",
      "typescript": "~3.8.3"
   },
   "description": "An Ionic project"
}

EDIT: I did not mention this in the initial question but the D: drive is a ram disk. Ultimately this ended up being very important information and I updated the question to include this and the ramdisk tag so hopefully others will find this solution quicker than I did in the future.