Failed to load resource: the server responded with a status of 502 (Bad Gateway)

How can you solve a 502 error? I purposefully put a syntax error in my code to spot what line of code is causing the 502 error. (if the 502 error is caused before the syntax error it means the line causing the 502 is before the line of code containing the the syntax error)

I believe whats causing the 502 error is a nested loop that contains heavy calculations. It would take up to 2 minutes for it to finish that block of code on my local server. However on a public server I just get this 502 Bad Gateway nginx/1.10.3 (Ubuntu)

My site is made with django. I am also using numpy (i installed it on the public server), js, html, and css.

Any ideas for where to start looking to solve this error?