Comment # 1 on bug 972067 from Bernhard Wiedemann

That sounds more like the typical btrfs behaviour,
but if it is really ext4, you want to check

tune2fs -l /dev/sda3 | grep "Reserved block count"

or whatever is your partition containing the filesystem.

By default, 5% of the total size is reserved for the root user
so if you are missing 60GB, that could be normal,
if the total filesystem size is around 1200GB.

you can adjust this value using tune2fs -m or -i