It seems that enabling Lazy Load Images in LSCache resolves the problem.
I investigated as you suggested; however, the form field is blank (in fact, it’s disabled).
UPDATE: I looked under the “Comments” field (for one of the forms) and the “Message” field (for the other form) and I found the text and removed it. Thank you!!
http://prayerbook.ca/connect/contact/
and
http://prayerbook.ca/membership/
I checked the ‘Change Error Messages,” as you suggested, but the “Please complete the CAPTCHA” field is blank.