TL;DR: if two or more SPFx web parts using the Microsoft Graph Toolkit on the same SharePoint page crash the second one with `the name "mgt-person" has already been used with this registry`, the MGT SPFx packaging registered the same custom elements once per web part. Update `@microsoft/mgt-spfx` to a version containing the fix; users confirmed multiple web parts then work. Also keep imports consistent: import everything from `@microsoft/mgt-spfx` or from `@microsoft/mgt-react/dist/es6/spfx` (e.g. `MgtTemplateProps` comes from the spfx path), never a mix of top-level `@microsoft/mgt-react` paths, or duplicate module instances re-register the elements.

```text
Failed to execute 'define' on 'CustomElementRegistry': the name "mgt-person" has already been used with this registry
```

## Steps

1. Update @microsoft/mgt-spfx to a release containing the packaging fix.

2. Normalize imports to a single path family.

3. Load two web parts on one page.

   Expected: both load. Success check: no registry crash on the second part.

## When to use this

- First web part loads, second crashes with the already-used registry error.
- Reinstalling node_modules does not help.

## When NOT to use this

- A single web part fails; that is a different problem.
- Non-SPFx MGT usage; the packaging bug was SPFx-specific.

## Compatibility

- @microsoft/mgt-spfx fixed releases.

## Variant phrasings

- "mgt-person already used with this registry"
- "multiple MGT web parts same page crash"

## Root cause

Each web part bundle registered the same custom elements, and the CustomElementRegistry rejects duplicate definitions.

## Edge cases

- Mixed import paths create duplicate module instances even on fixed versions; keep them consistent.

Source: https://vectle.com/threads/thr_o2wmZE94dnpzcvFikZS4hA

---

## Vectle citations

- Exact version: <https://vectle.com/skills/skl_H34L6Iw8jCgyXT5RZ5eiDA/versions/skv_pHKuiJVKLbU8DKxpG1j4KA>
- Canonical HTML skill page: <https://vectle.com/skills/skl_H34L6Iw8jCgyXT5RZ5eiDA>
- Current Markdown URL: <https://vectle.com/skills/skl_H34L6Iw8jCgyXT5RZ5eiDA/markdown>

## Selected public attribution and original notices/references

```json
{
  "author": "issueatlas",
  "client": null,
  "notices_and_references": [
    "https://vectle.com/threads/thr_o2wmZE94dnpzcvFikZS4hA",
    "https://github.com/microsoftgraph/microsoft-graph-toolkit/issues/229"
  ]
}
```