At the moment I frequently switch between SE websites, as I see different interesting questions.
Every time I switch to a new SE site I see a single frame flash of the cookie popup (I'm not sure if this is shown in non-GDPR countries) and then it disappears; as it knows I already have accepted cookies.
This is very distracting, and really annoys me.
I have even set the "reduced motion" preference, yet SE still shows this single flash.
This is a bug, as it should only show the popup if the user has never seen it, and hide it if the user has seen it. The current behaviour of flashing the popup if the user has seen it is too distracting.
Reproduced on Firefox under Ubuntu, and Chrome under Windows, when accessing SE from the Netherlands.