How to I troubleshoot a deploy that is forever in "IN_PROGRESS"?

I'm using ECS with Fargate, I have a service running and it is working OK. But after I update the task definition (new deploy) and the console (ECS -> Clusters -> Tasks tab) shows that my current task is INACTIVE, which is normal, but it doesn't show any new task being created, nor any stopped task, even after an hour. It is as if ECS is not trying to run my new definition.

If I use the awscli to find information about my service:

aws ecs describe-services --cluster cluster-xxxxxxx --services service-svc-xxxxxxx --region us-east-1
It has two deployments. The first is alright, it is the running deployment. The most recent one, it shows:

          "desiredCount": 1,  
          "pendingCount": 0,  
          "runningCount": 0,  
          "failedTasks": 7,  
          ...  
          "rolloutState": "IN_PROGRESS",  
          "rolloutStateReason": "ECS deployment ecs-svc/XXXXXXXXXXXXXXXXXX in progress."  

Again, there is nothing on the ECS console that points to failed tasks. It is as if the task is failing on a so premature state, its not even logging anything. On the "Task" tab, when I point "Desired task status:" to "Stopped" it shows an empty list with "No Results".

I tried looking at CloudTrail event, but there is nothing there about failed tasks. On CloudWatch, the logs for container insights (/aws/ecs/containerinsights/cluster-xxxxxxx/performance) also don't mention failing tasks.

How can I troubleshoot this situation?