Very recently, the reCaptcha widget is experiencing anomalies. In some scenarios it works on some browsers and not others (on the same machine). This may appear as either the widget saying the 'token' is invalid for the domain, and not allowing it to be checked off. Or it may appear to work, but 'validation' fails. Though it wasn't reported until after the release/upgrade to v2.4.0patch1 (reCaptcha implementation updated to support anti-spam multiple widgets per page), it also occurs on v2.4.0 systems and possibly older.
first issue was a server related issue involving php openssl setup which created a certificate issue during the validation process
second issue seems limited to Firefox based browsers and may be related to cookies or cache which provides incorrect domain information to Google for displaying the reCaptcha widget
Very recently, the reCaptcha widget is experiencing anomalies. In some scenarios it works on some browsers and not others (on the same machine). This may appear as either the widget saying the 'token' is invalid for the domain, and not allowing it to be checked off. Or it may appear to work, but 'validation' fails. Though it wasn't reported until after the release/upgrade to v2.4.0patch1 (reCaptcha implementation updated to support anti-spam multiple widgets per page), it also occurs on v2.4.0 systems and possibly older.