How to delete Web ACLs associated AWS resoureces BUT which has been already removed?

In WAF & Shield page, I can't delete a Web ACL which is associated with a Cognito User Pool. The Cognito User Pool is already removed when an Amplify app was removed. The Cognito User Pool was generated by Amplify automatically.

In this situation, when you go to WAF & Shield page > Web ACLs > Associated AWS resource in AWS console, you can see the error message below.

Error An unspecified error occurred. Check your network connectivity.

You cannot unassociate the resource, so you cannot delete the Web ACL. How should I do? Thanks in advance.