ECS task: Getting error 'No space left on device', when only using 15% of ephemeral storage

Hi all, running a .NET app in a Linux ECS task (fargate). It is configured with 100GB of ephemeral storage and I'm getting a 'No space left on device' error when it hits 15.7% utilisation (according to container insights).

Anyone know what's going on here?

Here's the task definition:

{
"taskDefinitionArn": "*****",
"containerDefinitions": [
    {
        "name": ""*****",
        "image": ""*****",
        "cpu": 0,
        "portMappings": [],
        "essential": true,
        "environment": [
           ...
        ],
        "mountPoints": [],
        "volumesFrom": [],
        "logConfiguration": {
            "logDriver": "awslogs",
            "options": {
                "awslogs-group": "/ecs/"*****",
                "awslogs-region": "eu-west-2",
                "awslogs-stream-prefix": "ecs"
            }
        }
    }
],
"family": ""*****",
"taskRoleArn": ""*****",
"executionRoleArn": ""*****",
"networkMode": "awsvpc",
"revision": 1,
"volumes": [],
"status": "ACTIVE",
"requiresAttributes": [
    {
        "name": "com.amazonaws.ecs.capability.logging-driver.awslogs"
    },
    {
        "name": "ecs.capability.execution-role-awslogs"
    },
    {
        "name": "com.amazonaws.ecs.capability.ecr-auth"
    },
    {
        "name": "com.amazonaws.ecs.capability.docker-remote-api.1.19"
    },
    {
        "name": "com.amazonaws.ecs.capability.task-iam-role"
    },
    {
        "name": "ecs.capability.execution-role-ecr-pull"
    },
    {
        "name": "ecs.capability.extensible-ephemeral-storage"
    },
    {
        "name": "com.amazonaws.ecs.capability.docker-remote-api.1.18"
    },
    {
        "name": "ecs.capability.task-eni"
    }
],
"placementConstraints": [],
"compatibilities": [
    "EC2",
    "FARGATE"
],
"requiresCompatibilities": [
    "FARGATE"
],
"cpu": "2048",
"memory": "10240",
"ephemeralStorage": {
    "sizeInGiB": 100
},
"registeredAt": "2023-10-10T11:11:17.864Z",
"registeredBy": ""*****",
"tags": []
}