clipper: How to debug cause of "ImportError when running Container"

I am a bit stuck: I’m trying to deploy a pytorch model which runs fine on my local computer but hangs when trying to deploy it. The model’s docker container gives me this error log:

$ docker logs 4437076d479c
Starting PyTorchContainer container
Connecting to Clipper with default port: 7000
Encountered an ImportError when running container. You can use the pkgs_to_install argument when calling clipper_admin.build_model() to supply any needed Python packages.

It seems like it is not able to import some dependency. I installed the same model in a clean anaconda environment on my computer and checked exactly which dependencies I needed to install. I listed these in pkgs_to_install. I have inspected all the log files of the docker containers and I can’t find the actual error message which could give me a hint as to which dependency is missing. May some error log be getting swallowed somewhere?

The model I’m trying to run is the xinntao/ESRGAN for image super-resolution.

Dependencies: Python 3 PyTorch >= 0.4.0 Python packages: pip install numpy opencv-python

The command to deploy the model:

deploy_pytorch_model(
    clipper_conn,
    name="superresolution-model",
    version=1,
    input_type="bytes",
    func=image_enhance,
    pytorch_model=model,
    pkgs_to_install=['opencv-python','numpy','six', 'Pillow','wheel',]
    )

the clipper_service.py is where I define the model and try to deploy.