Disk full but without reason found

**Operating system:CentOS
**OS version:7

Hi, df -h shows full disk,

Filesystem Size Used Avail Use% Mounted on
/dev/sda3 191G 176G 16G 92% /

Partition Table: loop

but by checking with ncdu and folder by folder, the reason for used space can’t be found.
Do you have any ideas or faced similar issue? Thank you!