hard drive – Unallocated Space after BootCamp not restored to main HD


I am unable to reclaim 1 TB of Unallocated Space to my main HD. Neither Disk Utility or BC-Assistant succeeds in restoring it to a single partition. Disk utility error message

Disk Utility unallocated space

The process starts and fails, please is there anyway to get my 1 TB back to my main HD?

I cannot see the 1 TB Unallocated Space in ‘diskutil list’:

diskutil list output

Please, can someone explain what needs to be done to get the 1 TB back? My main HD is a fusion drive and should be 2 TB.