formgrader doesn't work

[bpfrd]

Hi
I deployed jupyterhub & nbgrader in kubernetes. I'm using this version of nbgrader https://github.com/CERIT-SC/nbgrader-k8s
please find the issue and details below:

Operating system

Centos

nbgrader --version

nbgrader version 0.9.2

jupyterhub --version (if used with JupyterHub)

jupyterhub version 3.0.3

jupyter notebook --version

jupyterhub notebook version 7.1.2

Actual behavior

Formgrader stopped working recently and none of its functionalities, e.g., autograde, release feedback, manual grading, etc work! It doesn't give any specific errors. it shows something like "there is an error in autograding...." However, the command line works. but manual grading is not possible with the command line. I was wondering how i can debug it?

best regards