Backing up C drive does not seem to be complete

When I backup my C drive with UrBackup, the entire image only spent around 25 GB on the disk. This is a 2 TB SSD that is almost completely full. The D drive backed up completely, spending an expected 500 GB of space. How can I resolve this issue?

How did you check the size occupied on the server?

Was the backup full or incremental?

Which image file format did you choose?

It was a full backup, the first those machines ever made. The backup sizes were checked on disk on the machine. The file format was kept the default, which I believe is compressed VHDX.

It is unlikely that a bit less than 2TB of data was able to compress to 25GB.

What does the log say? (help with logs)