Forms not redirecting and forms eternally showing "Waiting" as button text. Contacts ARE created

Your software
My Mautic version is: v4.0.1
My PHP version is: 7.4
My Database type and version is: mysql Ver 15.1 Distrib 10.3.27-MariaDB, for Linux (x86_64) using readline 5.1

Your problem
My problem is: Forms not redirecting (if redirect is set) and forms eternally showing “Waiting” as button text and not displaying success message (if display message is set). Note: Contacts ARE being created, so that part is working. How can I fix this?

Page that has form with success message set up (but not is not displaying message when submitted): https://sellonautopilot.com/

Page that has form with redirect set up (but not is not redirecting when submitted): {Course waitlist} Market Research, Strategy, Go! - Sell On Autopilot

These errors are showing in the log:

Steps I have tried to fix the problem: