@Megan I think it’s to do with how Google detects the spam risk.
If it scores high it’ll provide more challenges to the user.
As to what affects the score, I have no idea, but it’s likely to be many factors like IP address, browser, location, user history, the domain, site history, etc…
I’ve found that this happens more so in Safari. Whether that’s because I’m not logged into my Google account when in Safari or because it’s harder for Google to detect various settings for it’s scoring system… I don’t know.
Bottom line, I don’t think there is much you can do about it. But interested if anyone else has further insight into this.
Perhaps Treepl can adjust the spam score for your site, similar to how we have the spam score setting for recaptcha v3 in the admin?