Missing available space in device block (size != used + available)

Question

So, there is this device block which has 654G of total size, of those 579G are being used, but only 42 is Avail (it should be 65G available!)

$ df -h /dev/mapper/cryptdata
Filesystem             Size  Used Avail Use% Mounted on 
/dev/mapper/cryptdata  654G  579G   42G  94% /data
$ du -sh /data
579G    /data

What is wrong here? I suspect maybe it has to do with Filesystem integrity or LVM (Logical Volume Manager).

What I need is to correct this error so it should have 65G available, but I don't know how.