Recaptcha "response token is empty"

website: onsitepoweradvisor.com
GP version: Premium 2.03

Email form submissions via Contact Form 7 (version 5.4.2) fail. Two CF7 forms on this site, both fail to submit messages. The user sees an orange box with error message "There was an error with you message, try again later".

Using Flamingo, I see these form submissions flagged as spam, and the reason as: "Spam log: reCAPTCHA response token is empty."

I disabled ReCaptcha and the form submissions went through ok.

The FAQs on CF7 point to possible theme issues: https://contactform7.com/faq-about-recaptcha-v3/#response-token-is-empty

I have purged the entire site cache, all active plug-ins are current and compatible with current WP and PHP versions.

The site currently has ReCaptcha enabled.

Please let me know if you can recommend any steps to resolve this issue.