When Global Optimization fails, the issue is often related to data quality, scheduling configuration, or constraint validity rather than user permissions. Field Service provides a built-in diagnostic tool to surface such issues.

Option D is correct. The 'Health Check' tool, when run with 'Horizon Based Validations', evaluates the data, Scheduling Policy, Operating Hours, Service Resources and Service Appointments in scope of the optimization run. It surfaces issues such as missing geolocations, invalid time slots, missing skills, and inactive resources, which are common causes of optimization failures.

Option A is incorrect because logging a support ticket should be the last resort, not a first troubleshooting step. The admin should first attempt to identify the root cause using built-in diagnostics.

Option B is incorrect because Permission Sets are required for users who initiate optimization, but the question already confirms that the 'Optimization User' is active. Permission Sets would prevent the optimization from starting, not cause it to fail mid-run.

Option C is incorrect because if Optimization were not enabled, the dispatchers wouldn't be able to invoke it at all.