Checking around the web it seams like this is a common problem with reCaptcha Invisible and v3. So it's likely a problem on Googles end to be fixed, but have added a bug ticket to take a deeper look to see if some sort of workaround can at least be implemented.
forge.joomlapolis.com/issues/7693
It's also entirely possible people are spending too much time on your registration form. Then by time they submit it the captcha session has expired. Unfortunately we've no control over this as that's entirely up to Google, but the solution is typically to streamline registration so users don't spend significant amount of time trying to join your site by only asking what is absolutely needed in that moment while letting the rest be filled out in profile edit.