Seeded backup never finishes

the status page of my server says that there was never a file backup. However, I know that the backup job ran for a few days. I actually never saw the job finishing, but running close to 100% on the activity page.
Every day (as configured), a new backup is started, backing up (I assume) new or changed files. These files make up around 3 GB, while the initial backup was 300 GB.
The client is connected as an internet client and the backup was a seeded backup (due to the huge amount of data i transfered the data to a hard-disk, connected the hard-disk to a local client and configured the client to backup the data.).
Any idea what is wrong here?
Thank you in advance!