LCP element and ALLS diagnostics give an Error though working on web.dev/measure

[exkalation]

Provide the steps to reproduce

1. Run LH on https://web.dev/optimize-cls/ (without any flags, but also with --preset perf as well as headless)

What is the current behavior?

The diagnostics for

• Largest Contentful Paint element
• Avoid large layout shifts

both show "Error!" as can be seen in this screenshot:

There are some errors/warnings on stdout that seem to be related:

  status Gathering: TagsBlockingFirstPaint +6ms
  status Gathering: TraceElements +4ms
  method <= browser ERR:error DOM.resolveNode  +33ms
  status Disconnecting from browser... +56ms
  status Analyzing and running audits... +13ms
  status Auditing: First Contentful Paint +6ms
  ...
  status Auditing: Minimize third-party usage +1ms
  status Auditing: Largest Contentful Paint element +98ms
  Runner:warn TraceElements gatherer, required by audit largest-contentful-paint-element, encountered an error: Protocol error (DOM.resolveNode): Node with given id does not belong to the document +1ms
  status Auditing: Avoid large layout shifts +0ms
  Runner:warn TraceElements gatherer, required by audit layout-shift-elements, encountered an error: Protocol error (DOM.resolveNode): Node with given id does not belong to the document +1ms
  status Auditing: Uses efficient cache policy on static assets +1ms
  status Auditing: Avoids enormous network payloads +2ms

What is the expected behavior?

• "Largest Contentful Paint element" should say "1 element found", giving the respective HTML
• "Avoid large layout shifts" should say "No elements found"

As can both be seen in this screenshot taken from a report generated on https://web.dev/optimize-cls/, where this seems to work despite this issue:

Full web.dev report available here:
https://lighthouse-dot-webdotdevsite.appspot.com//lh/html?url=https%3A%2F%2Fweb.dev%2Foptimize-cls%2F

Environment Information

• Affected Channels: CLI (PowerShell, as well as on WSL1)
• Lighthouse version: 6.0.0
• Chrome version: 83.0.4103.61 (Official Build) (64-bit) (cohort: Stable)
• Node.js version: 12.17.0
• Operating System: Windows 10, Build 1909

Related issues
Potentially #10869

[patrickhulce]

Thanks for filing @exkalation! #10873 is related and #10877 fixes this.

[exkalation]

Thank you @patrickhulce for your quick response. Can you confirm whether this issue has an impact on any measured metrics?

[patrickhulce]

Confirmed this issue has no impact on the performance score or the metric values themselves, it just makes it harder to debug why they are what they are :)

[exkalation]

Very good, thank you very much!