Hi Faisal,
I didn't try but you may try below option as I don't have any invalid FF log reports in my system.
Also make sure when you have 4007 parameter set as YES, schedule only Log sync job and don't schedule Workflow sync job as this is one of the reason for invalid FF log report.
Go to GRACFFLOG table and pull out the FFLOG_ID value based on FF ID or Date or any other criteria with WORKFLOW_SENT as X
Then go to GRACFFREPMAPP table and input the FFLOG_ID values and check if there is any ACTION_ID associated with those FFLOG_ID entries
If the ACTION_ID doesn't exist for any FFLOG_ID means that Workflow is sent and no data is present in that FF Log workflow.
These reports are called Invalid FF Log reports
Based on ACTION_ID you can check the Action details from table GRACACTUSAGE table.
Please check and let me know 
Regards,
Madhu.
