WordPress/Divi Form & Email Deliverability Debugging

Background A website built on WordPress with the Divi theme runs two business-critical lead forms (a booking/appointment form and a product order form). For several weeks now, both forms have been behaving in an unstable and inconsistent way. In a structured test with 6 people across multiple days, devices, and browsers, 5 of the 6 testers encountered errors — each time in a different combination. Lead volume has dropped measurably over the same period. Specific Symptoms Despite a success message shown in the frontend, submissions are sometimes not stored in the backend (Form Entries). Confirmation and admin notification emails go out only in some cases. A time-selection dropdown in the booking form is intermittently unusable/blocked. There is also a 24-hour lead-time rule for appointments that needs to work reliably. Your Task Reproduce and perform root-cause analysis of the inconsistent submission behavior (frontend JS, AJAX/REST submit, caching/CDN, plugin- and server-side logging). Diagnose the unreliable email delivery (SMTP configuration, mail server logs, possibly a missing transactional-email setup). Fix the dropdown bug and ensure the 24h rule works. If the existing form setup (Divi forms or the plugin in use) cannot deliver a stable result, evaluate and cleanly migrate to a proven premium plugin (e.g. Gravity Forms or WS Form Pro), including data migration and email routing. Finally, document the root cause and verify the fix with a repeated test run across different browsers and devices. Requirements Proven experience with WordPress and Divi as well as form plugins and their submission/hook logic; solid command of PHP, JavaScript/AJAX, and the WordPress REST API; strong understanding of email deliverability (SMTP, SPF/DKIM/DMARC, transactional mail); experience debugging caching-related issues (page cache, object cache, CDN); and a structured, traceable approach with clean documentation. Nice to Have Experience with Gravity Forms / WS Form Pro, conversion/lead-funnel understanding, and tools like Microsoft Clarity for user-behavior analysis. Deliverables A working, stable submit flow for both forms with reliable backend storage and email delivery, a short root-cause report, and a documented verification test. Important Constraint Before any updates or changes, existing integrations and Divi sections must be checked — previous updates broke frontend rendering. Please make no untested changes on the live site. If you read this start your Message with "Orange"