With reCaptcha V3 enabled, when registering and submitting the registration form the following error message appeared at the bottom of the screen:
Could not connect to the reCAPTCHA service. Please check your internet connection and reload to get a reCAPTCHA challenge.
The browser console indicated it was caused by a cross scripting error. It appears that if you are calling reCaptcha from http instead of https this introduces the cross scripting issue. Changing the board to use and force https solved the issue.