(Weird, the site removed my post and replaced it with the title...)
Visit this web page: https://www.gov.uk/guidance/the-product-security-and-telecommunications-infrastructure-psti-bill-product-security-factsheet
Scroll down to near the bottom of the page, and note the horizontal bar at the bottom starts flashing quickly. This doesn't happen in Safari. It happens in compatibility mode.
Orion build Version 0.99.108.1-beta (WebKit 613.1.10)
Mac OS 12.1 public beta
gp Bad news (or good news!) is that I can not reproduce it?
Me neither now, must have been a bug on the site. Let's close for now.