I've attached an image of the issue. The Data drive D: has 1 TB partitioned to it, however at the top you will see it only shows 436 GB of storage available.
We used a backup to restore this drive, and since then it hasn't allowed us to extend the drive. If you try and shrink the drive even by 1 MB, if gives you an incorrect parameter error. chkdsk was run and reports no errors or bad blocks.