Regularly happening on my iPad, a few times it’s sort of half appeared when changing pages on a thread, this causes everything to lock so I have to click back to get rid.
Cookies expire on Safari after 1-7 days (depending on a few things), meaning you'll get the popup every week.
Since joining the paid NSC 1901 I've not had a problem, and, reading the terms of membership, if I do have a problem @Booza comes around and clicks "ACCEPT" for me.
Any Booza in particular ? Plenty on here to choose from according to the Friday night drinking thread.