Provide the steps to reproduce

1. Run LH on https://bonusi.soft-press.com/ https://splighthouse.marti.bg (or on https://bonusi.soft-press.com/all https://splighthouse.marti.bg/all)
   • DevTools: with Simulated throttling turned off
   • web.dev: as it is
2. Observe the CLS metric and "Avoid large layout shifts."

What is the current behavior?

The CLS jumps from 0 to seemingly random higher value, despite no visible layout shifts in the preview pane. The value is higher on web.dev than on DevTools. "Avoid large layout shifts" returns "Error!", or gives different elements on every run. See screen recordings.zip

What is the expected behavior?

The CLS should stay at 0, as it does with Simulated throttling on.

Environment Information

• Affected Channels: DevTools, web.dev "Test my site"
• Lighthouse version: 6
• Chrome version: 85.0.4159.0 (Official Build) canary (64-bit) (cohort: Clang-64)
• Node.js version:
• Operating System: Windows 10 64bit

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