CloudSyncTask FTP running for days and causing double of transfer data due to partial files on target

Hi Forum,

i wonder why my CloudSyncTask was replicating more data than i acutally have. So it started of good. replicating 400 of 500GB with 60MB/s ( 100MB is network limitation )

So loooking into a specific target directory, i can see that it only contains .partial files

Example:

This is the target NAS ( FTP Cloudsync)
-rwxrwxrwx 1 nas share 8209058 Mar 12 17:13 DSC_0665.JPG.kaxahaf7.partial
-rwxrwxrwx 1 nas share 8209058 Mar 12 03:52 DSC_0665.JPG.mipimad3.partial

This is from TrueNas
-rwxrwx— 1 truenas_admin 8209058 Feb 12 16:42 DSC_0665.JPG*

However the partial files have the identical Size as the original File. So i dont get what its acutally doing. Is i leaking something?