Ember build error: EEXIST: file already exists

I am trying to update an Ember/Ruby on Rails project that has not been deployed in two years (it's still happily running well in production, but new deploys fail).

I got the Ruby on Rails part to update, but Ember I am less familiar with and struggling, currently stuck on this error:

Build Error (TemplateCompiler)

EEXIST: file already exists, symlink '/var/folders/8m/vxpf7qd11fg7gn7ps0dyx_pc0000gn/T/broccoli-92657dOMHa3WeZnd7/out-335-funnel_funnel_ember_bootstrap_addon/ember-bootstrap/components/bs-accordion.js' -> '/var/folders/8m/vxpf7qd11fg7gn7ps0dyx_pc0000gn/T/broccoli-92657dOMHa3WeZnd7/out-336-template_compiler/ember-bootstrap/components/bs-accordion.js'

I have found similar errors online but none of the suggested fixes worked for me. I have the latest version of bootstrap, ember-bootstrap, broccoli-asset-rev and ember-cli. The files mentioned in the error are not from my project, as far asa I can tell they are from the ember-bootstrap package.

Current package.json inside app-ember:

{
  "name": "app-ember",
  "version": "0.0.0",
  "private": true,
  "description": "Small description for app-ember goes here",
  "repository": "",
  "license": "MIT",
  "author": "",
  "directories": {
    "doc": "doc",
    "test": "tests"
  },
  "scripts": {
    "build": "ember build",
    "lint:hbs": "ember-template-lint .",
    "lint:js": "eslint .",
    "start": "ember serve",
    "test": "COVERAGE=true ember test && rm coverage/coverage-summary.json && nyc check-coverage",
    "debug-test": "ember test --server"
  },
  "devDependencies": {
    "@ember/jquery": "^0.5.2",
    "@ember/optional-features": "^0.6.3",
    "active-model-adapter": "^2.2.0",
    "bootstrap": "^5.0.2",
    "broccoli-asset-rev": "^3.0.0",
    "ember-ajax": "^4.0.1",
    "ember-bootstrap": "^4.9.0",
    "ember-bootstrap-controls": "github:clevercase/ember-bootstrap-controls#v3.0.0",
    "ember-can": "^1.1.1",
    "ember-cli": "^3.27.0",
    "ember-cli-app-version": "^3.2.0",
    "ember-cli-babel": "^7.1.2",
    "ember-cli-code-coverage": "github:kategengler/ember-cli-code-coverage#v1.0.0-beta.8",
    "ember-cli-dependency-checker": "^3.2.0",
    "ember-cli-eslint": "^4.2.3",
    "ember-cli-htmlbars": "^4.3.1",
    "ember-cli-inject-live-reload": "^1.8.2",
    "ember-cli-moment-shim": "^3.7.1",
    "ember-cli-pretender": "^3.2.0",
    "ember-cli-rails-addon": "^0.10.0",
    "ember-cli-sass": "^10.0.1",
    "ember-cli-sri": "^2.1.1",
    "ember-cli-template-lint": "^2.0.2",
    "ember-cli-uglify": "^2.1.0",
    "ember-concurrency": "^0.9.0",
    "ember-data": "~3.14.0",
    "ember-data-change-tracker": "^0.8.0",
    "ember-export-application-global": "^2.0.1",
    "ember-freestyle": "^0.11.10",
    "ember-load-initializers": "^1.1.0",
    "ember-maybe-import-regenerator": "^0.1.6",
    "ember-moment": "^7.8.1",
    "ember-notify": "^5.3.0",
    "ember-percy": "^1.6.0",
    "ember-power-calendar": "^0.13.3",
    "ember-power-calendar-moment": "^0.1.7",
    "ember-print-this": "^1.0.0",
    "ember-qunit": "^3.4.1",
    "ember-resolver": "^5.3.0",
    "ember-route-action-helper": "^2.0.8",
    "ember-simple-auth": "^1.9.2",
    "ember-source": "^3.8.3",
    "ember-spreadsheet-export": "^0.4.0",
    "ember-steps": "^8.0.2",
    "ember-welcome-page": "^3.2.0",
    "eslint-plugin-ember": "^5.2.0",
    "loader.js": "^4.7.0",
    "lolex": "^3.1.0",
    "nyc": "^15.1.0",
    "popper.js": "^1.16.1",
    "qunit-dom": "^0.8.5"
  },
  "engines": {
    "node": "6.* || 8.* || >= 10.*"
  }
}