[Plugin: WP-reCAPTCHA] reCaptcha disallows users from leaving comments

Odd failure mode. With reCaptcha DISabled, users can leave comments without a problem. With reCaptcha ENabled, however, when the user fills out the form completely, and correctly identifies the words in the captcha, then clicks Submit, the page reloads but their comment does not appear, and reCaptcha does not present either error message. Additionally, the comment does not appear in the WP admin area in the list of comments awaiting moderation.

https://www.ads-software.com/extend/plugins/wp-recaptcha/