Semantic Release not recognising pkgRoot variable

Question

I am using Semantic Release with a private gitlab CI/CD, and getting the error when running the pipeline:

npm ERR! enoent ENOENT: no such file or directory, open '/builds/squint-nyc/bootstrap-in-a-snap/package.json'

The package.json is in a subfolder Packages/com.squintopera.unity.bootstrap/package.json as configured by the property pkgRoot in my releaserc.json below.

Am I doing something wrong, or is it a bug in SemanticRelease? Any help greatly appreciated.

{
  "branch": "master",
  "tagFormat": "v${version}",
  "plugins": [
    ["@semantic-release/commit-analyzer", { 
      "preset": "angular" 
    }],
    "@semantic-release/release-notes-generator",
    ["@semantic-release/npm", { 
      "npmPublish": true,
      "pkgRoot": "./Packages/com.squintopera.unity.bootstrap"
    }],
    ["@semantic-release/changelog", { 
      "preset": "angular",
      "changelogFile": "CHANGELOG.md"
    }],
    ["@semantic-release/git", {
      "assets": [
        "package.json",
        "README.md",
        "CHANGELOG.md",
        "Packages/com.squintopera.unity.bootstrap/**/*.*"
      ],
      "message": "chore(release): ${nextRelease.version} [skip ci]\n\n${nextRelease.notes}"
    }],
    "@semantic-release/gitlab"
  ]
}