Elastic Container Service Tags have stopped showing in cost explorer

This issue could be due to several factors. First, it's important to note that there can be a delay of up to 24 hours for newly activated cost allocation tags to appear in Cost Explorer. However, since you mentioned this has been ongoing since March 29th, it's likely not a delay issue.

Given that your resources are still correctly tagged and the tags are enabled on the payer account, here are a few potential reasons for this problem:

1. Account changes: If your account has recently moved between different AWS Organizations, your active tags may have been deactivated. In this case, they would need to be reactivated by the new management account.

2. Tag propagation: Ensure that tag propagation is still enabled for your ECS resources. Sometimes, changes in the AWS environment can affect tag propagation settings.

3. Billing cycle: The issue started on a Sunday, which could coincide with the end of a billing cycle. There might be a temporary glitch in how the tags are processed for the new billing period.

4. AWS-side issue: Given that you didn't make any changes and the problem occurred on a weekend, it's possible this could be an AWS-side issue that they're not yet aware of or haven't communicated about.

To troubleshoot:

1. Double-check that the cost allocation tags are still active in the management account of your AWS organization.

2. Verify that the resources are still incurring charges and that the charges are appearing in Cost Explorer (even if not properly tagged).

3. Check if the issue affects all tags or only specific ones.

4. Look for any AWS service health announcements or updates that might be related to this issue.

If the problem persists after these checks, it would be advisable to contact AWS support for further assistance. They can investigate if there's an underlying issue on their side that's preventing the tags from appearing in Cost Explorer.
Sources
Cost allocation tags are managed at the payer account level. | AWS re:Post
What are the reasons for Budget not working using cost filter with specific tags even after activating these tags in Cost Allocation Tags section ? | AWS re:Post