unable to access a lesson with 200 resources with kolibri-server

[lyw07]

Observed behavior

This is an issue reported on community forum:
https://community.learningequality.org/t/got-the-following-error-in-kolibri-today/1570

The user is getting error 414 (request uri too large) when accessing a lesson with more than 200 resources

Expected behavior

Users should be able to access lessons without errors, or restricted with creating a lesson with 200 resources

User-facing consequences

Users unable to access the lesson with 200 resources and also unable to delete it afterwards

Errors and logs

please see the details in the community forum post

Steps to reproduce

1. install kolibri-server
2. send a request to the url in the error message posted on the forum

Context

Version: 0.13.3
OS: Linux-4.19.69-v7±armv7l-with-debian-9.11
Python: 3.5.3
Installer: kolibri(apt) with kolibri-server Version: 0.3.8~beta2-0ubuntu1
Server: nginx/1.10.3
Database: /home/pi/.kolibri/db.sqlite3
Device name: raspberrypi

[lyw07]

Since the user uses Nginx, we suggested the user to change large_client_header_buffers to 9k in the Nginx config.
However, after changing the Nginx config, the 414 error (request uri too large) was gone but the lesson was still inaccessible with error 502 bad gateway

[lyw07]

this only happens in kolibri-server. Kolibri 0.13.3 alone doesn't have this issue