Update: I received the following reply from WF Support…
"I’ve checked your form and reCAPTCHA field in Webflow and it’s all set correctly.
This can sometimes appear even when everything is correctly configured on the frontend. It’s not specific to Webflow and can happen on other platforms as well. Occasionally, these warnings show up due to false positives on Google’s end or increased spam bot activity. If reCAPTCHA is functioning properly on your site, blocking spam and allowing legitimate users then this message can usually be ignored.
These warnings often go away on their own after a short time, especially if they are due to false positives."