🚨 Error: failed to attach shadow document for page: Failed to execute 'removeChild' on 'Node': The node to be removed is not a child of this node.

Details
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**Error report:** [link](http://go/ampe/CNSSoP7uhdSVDg)
**First seen:** Nov 18, 2020
**Frequency:** ~ 715/day

Stacktrace
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Error: failed to attach shadow document for page: Failed to execute 'removeChild' on 'Node': The node to be removed is not a child of this node.

    at removeChild (src/shadow-embed.js:183:15)

    at importShadowBody (src/multidoc-manager.js:246:23)

    at builder (src/multidoc-manager.js:205:4)

    at attachShadowDoc_ (src/multidoc-manager.js:235:11)

    at attachShadowDoc (extensions/amp-next-page/1.0/service.js:594:40)

    at attachDocumentToPage (extensions/amp-next-page/1.0/page.js:253:7)

    at attach_ (extensions/amp-next-page/1.0/page.js:208:11)

    at resume (extensions/amp-next-page/1.0/service.js:450:60)

    at map (extensions/amp-next-page/1.0/service.js:450:41)

Notes
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`@jridgewell` modified `src/shadow-embed.js:181-184` in #29033 (Jun 26, 2020)
`@wassgha` modified `src/multidoc-manager.js:232-273` in #25629 (Dec 10, 2019)
`@wassgha` modified `src/multidoc-manager.js:189-230` in #25629 (Dec 10, 2019)
`@wassgha` modified `src/multidoc-manager.js:232-273` in #25629 (Dec 10, 2019)
`@wassgha` modified `extensions/amp-next-page/1.0/service.js:594-601` in #26296 (Jan 23, 2020)
`@wassgha` modified `extensions/amp-next-page/1.0/page.js:252-257` in #26610 (Feb 11, 2020)
`@wassgha` modified `extensions/amp-next-page/1.0/page.js:208-208` in #26610 (Feb 11, 2020)
`@renovate-bot` modified `extensions/amp-next-page/1.0/service.js:450-450` in #27350 (Mar 30, 2020)
`@renovate-bot` modified `extensions/amp-next-page/1.0/service.js:450-450` in #27350 (Mar 30, 2020)

**Seen in:**
- 11-20 Beta (0012)
- 11-20 Experiment-A (0012)
- 11-20 Experimental (0012)
- 11-20 Stable (0012)
- +2 more

**Possible assignees:** `@jridgewell`, `@wassgha`

/cc @ampproject/release-on-duty