I ran into the same problem before, but with Django, not strapi/react. The cause for my issue was that I was using an anchor tag with a dummy link like , so by the time the sign-in pop-up would open, my main window's URL was something like "http://localhost:8000/#". This "#" at the end was causing the issue, and I fixed it by avoiding the "#" to be appended in the URL.

For those who are running in to similar error in Django, you need to explicitly set SECURE_REFERRER_POLICY in settings.py. Django's default referrer-policy is "same-origin", so give something like SECURE_REFERRER_POLICY = "no-referrer-when-downgrade" or SECURE_REFERRER_POLICY = "strict-origin-when-cross-origin".