$util.appendError is not working

This was working before, but I get no Graphql errors with $util.appendError. While debugging, the CloudWatch logs show the context has a property of 'outErrors' but no errors come back from the query. Am I missing something? I have it working in Amplify Mock correctly, but I can't get it on AppSync.

Start by reproducing the AppSync behavior described for $util.appendError and compare it with the working Amplify Mock behavior. Inspect the CloudWatch context and the GraphQL query response; the issue is resolved when appended errors are returned as expected or the AppSync limitation is documented.

Written by the indexing model from the issue text.