Multiple containers not behaving as expected

Hi guys! I am relatively new to Docker, I hope someone can help me. I have been stuck for days and I have read the relevant docker concepts

I have a script that spawns multiple containers (from a single image) with the same mounted data volumes; and same startup command (but this command has different arguments/parameters). This command takes in a videofile and process it with specified set of parameters.

The script takes care of assigning which videofile and what parameters to give to a container. Each container only process 1 videofile with a single set of parameters. Writes its result in a data volume with a distinct filename, then finally exits.

Containers spawn as expected but only the 1st configuration on each video gets processed (e.g. vid1+config1 and vid2+config1). Other containers with different configurations (e.g. vid1+config2, vid1+config3, vid2+config2 etc) do not finish as expected - output file gets lost

Any leads would be greatly greatly appreciated! I am btw running docker on ubuntu 16.04 and docker 1.13.1