There are two Contact Forms on a page of a site in Parallels Presence Builder . Captcha is enabled in one of them. On published side Captcha does not appear when typing in Message field.
The case has been submitted to the Plesk Service Team as an internal issue with the ID PPPM-1419 . The fix is planned to be included in a future update.
As a workaround enable Captcha in both Contact Forms .