Turnstile checkmark appearing twice (one success and one failure)

A user of our website sees the checkmark appearing twice, a success and a failure side by side like in the attached screenshot. He is unable to access the website as a consequence.

Einloggprobleme 3

Any clue what might be causing this?
I don’t think this is due to an initialization error on our side because we have a large traffic base and this is the only such report.

Any help would be appreciated
Thank you

If only one user is having this issue, it may be caused by the browser they are using. Have you asked the user to clear their cache or try to access your site using private browsing?