Bug report: exercise created in Kolibri Studio not loading

We found a bug when loading an exercise created in Kolibri Studio to our Instance.

The resource will not load within its frame (spinning wheel) and the log reports a 500 server error.

This error has started to occur after one of our users completed the exercise as part of a lesson and was re-assigned the same exercise in a later lesson.

Newly created student accounts can access the exercise and complete questions. However, if they navigate away and then attempt to open it again, the browser is unable to load the exercise (they just see a spinning wheel). This problem persists even if the user logs out and back in. Problem spotted on all devices tested.

Other exercises (e.g. from Khan Academy) load fine, even after multiple attempts at opening them. Screenshot below. The spinning wheel occurs where the system catches an Uncaught (in promise) error.

Tech specs:
Version: 0.12.1
OS: Linux-4.15.0-47-generic-x86_64-with-Ubuntu-18.04-bionic
Installer: apt
Server: Kolibri internal server
Database: /var/kolibri/.kolibri/db.sqlite3
Device name: watobe-2019-1-ubuntu-s-1vcpu-1gb-lon1-01
Free disk space: 21 GB
Server time: Mon Apr 08 2019 12:47:04 GMT+0200 (South Africa Standard Time)

Thank you for the report! I’ve filed an issue and we will follow up here if we need more information.