You make some changes, then the ECS Service tells you
The closest matching container-instance ... is missing an attribute required by your task.
Are you running the ECS agent on your own AMI? Maybe you need to update its config to enable some features that are enabled on the amazon AMI but not on by default in the agent.
In our case, we added an IAM role to the task, but this functionality isn't enabled by default. As a result, ECS would refuse to deploy on any of the instances on our cluster. We had to update our AMI with a new config.