Hi,
Can you please share your web link, so I can view your form and test why it's crashing. As you mentioned there are multiple logic e.g calculation e.t.c, can you please let me know all logic in form. So maybe I will develop a custom form for you. So it will be fast and reliable :)
A little intro about me: I have 5 years of experience in web development using PHP and MySql. I have developed multiple websites and web applications. I have also worked with multiple APIs.
Ping me back, so we can discuss about your form :)
Thanks and Regards,
Nabeel Abid