[CentOS] du, df (other tools?) way of reporting file/system sizes

hi guys. I have two virtually identical hardware boxes which report qcow2 sizes differently:

-> $ du -xh /00-VMsy//enc.vdb.back1.proxmox.qcow2 2.9G    /00-VMsy//enc.vdb.back1.proxmox.qcow2

-> $ du -xh /00-VMsy//enc.vdb.back1.proxmox.qcow2 71G    /00-VMsy//enc.vdb.back1.proxmox.qcow2

I checked I though obvious places: ext4 header shows the same features, I also looked at NVMes which all are formated with the same block size, mountpoins mount the same way. But, I must be still missing something... trivial? I'm thinking - perhaps some kernel tunables - but if so, which ones I cannot find. 'ls' reports the same everywhere, virtual 71G size. (so with spares) All thoughts shared are much appreciated. thanks, L.