This is most likely not it, but just to eliminate it, I'll ask anyway. The window asking to accept cookies is in the bottom left corner. (But I never saw it disappear immediately, as you describe.) You can find screenshot in many places: google.com/… - such as meta.stackexchange.com/q/359358, meta.stackexchange.com/q/362694, meta.stackexchange.com/q/362091, There is also a post on this meta - but without a screenshot: meta.mathoverflow.net/q/4954 — Martin Sleziak Apr 2 at 6:51

Although I see this bug report which might look a bit similar to yours: Cookie dialog popup flashes for a moment even when I've already accepted all cookies. However, it is marked as (status-norepro). — Martin Sleziak Apr 2 at 6:57

Do you have any browser add-ons, does it happen across browsers, across computers? Which browser, which operating system? What was the phase of the moon when you first noticed the symptoms? Were you recently stung by Africanized honey bees? Most of these questions should be answered already when submitting a bug report. — Asaf Karagila ♦ Apr 2 at 7:27

Yes it was the cookie business, it showed up after I switched off my adblocker. Thanks Martin and Asaf for pointing me in the right direction. Maybe you can also advise what to do with this question? Provide an answer, mark it as duplicate, migrate to SE meta, or just delete it? — მამუკა ჯიბლაძე Apr 3 at 5:57

@მამუკაჯიბლაძე I don't see closing as a duplicate as an option - we would need a duplicate target here on MathOverflow Meta and I do not see such a post. If you think that it might help somebody else who runs into the same problem, then it seems quite reasonable to write an answer (with an explanation what was actually the problem and how it can be solved). But it's your question - so it's your call. (Or you might simply wait to see whether some MO users chime in to respond to your most recent comment.) — Martin Sleziak Apr 3 at 9:59

@MartinSleziak OK, I will wait a couple of days then — მამუკა ჯიბლაძე Apr 3 at 10:02