I've been getting this too, authenticator prompts saying "logged in" and asking for confirmation, but no history whatsoever when I went to security to check.

It freaked me out the first time, I went through all the security settings I could find, but it was if it never happened.

I just ignored it the second time, but it's a bit unsettling, because the default authenticator flow also has the chance of accidentally hitting the right number.