Version: 54.0.2790.0 (Official Build) canary (64-bit)
OS: Mac OS X

What steps will reproduce the problem?
(1) Go to  https://www.rhs.org.uk/
(2) Scroll quickly (or use a slow network)

What is the expected output?
Reflow caused by a "this site uses cookie..." notification is mitigated

What do you see instead?
The reflow is not mitigated

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