This looks like a configuration problem in Case Lifecycle. Is your child case configured completely? I agree with Patrick. When you case configuration is not complete, you will run into this kind of issues.
The screenshot above is correct. Please make sure in the Cases Explorer that Benefits Enrollment is indeed a child case of Onboarding first. This can be verified by seeing that Benefits Enrollment is "indented" under Onboarding in the Cases Explorer (see attached TopCaseSubCase-CasesExplorer.png)..