Using Safari on iOS, this still pops up frequently. I've also noticed it on MacOS. Just this site though. The only extension I have running is Wipr. Turned it off for a few days, but no change.
I've haven't had that happen on Mac before. An extension like Wipe could be an issue but you've already tested that.
I have been using 2FA for years and that trusts a certain device for an extended period of time. I'm not sure if that affects your cases but may be good to try out.
I don't browse much on iOS but the handful of tries I've done have been fine.