Some computers report disk size and freespace in GB instead of MB.
Some clients are misreporting disk size values in GB instead of MB for the SMS_G_System_LOGICAL_DISK.Size and SMS_G_System_LOGICAL_DISK.FreeSpace fields.
Please see attached image. The highlighted record in SCCM displays as 464MB total and 422MB free space. The foreground image shows the actual disk management console with 464GB and 422GB respectively.
Thank you for your feedback. We have opened a bug internally to track this issue.