AWS CodeDeploy detected that the replacement task set is unhealthy?

Question

I have an ECS Fargate app up and running on AWS, and I was deploying a newer version of my code through CodeDeploy blue-green deployment. I have been using this method for quite some time, and I have never encountered any problems before unless there was actually a problem with the app itself. As always, I initiated the deployment and waited until all the tasks were running, and checked that the traffic has been rerouted to the newer version of task sets. I tested the app on a couple of devices and made sure that it was working correctly. However, after around 20 minutes or so, my service was down for a few minutes and I get an error message like this on CodeDeploy : CodeDeploy detected that the replacement task set is unhealthy. I expected codedeploy to automatically roll-back the deployment, but it was still the newer version of task set that was receiving traffic, and it was working fine! I did see a couple of stopped tasks but I do not have access to their logs anymore since stopped tasks somehow evaporate and are not accessible after some time. I re-ran the deployment with the exact same task definition, and that worked fine too. Does anyone have any idea what might cause a task set to be in an unhealthy state? Thanks so much! below is the image of the error deployment status