Soft Credit report fails when Only Full Group By is enabled
This is replicable by running the report with no changes to defaults on dmaster.
The cause is that the Soft Credit report overrides
CRM_Core_Form::postProcess() and calls
CRM_Core_DAO::executeQuery() directly instead of
CRM_Core_Form::buildRows(), which the FGB safeguards exist. So even though the report is marked as not optimized for FGB, it makes no difference.