Lars_Kohler, in your initial post you indicated you were trying to sync between two computers without syncing to the My Cloud using the WD Sync software.
“I am trying to set up a sync between a folder on my home PC and a folder on my Work PC, via the “WD Sync”-App.”
As explained the WD Sync software does not allow for syncing between two computers independent of the My Cloud. What it does do, which you found out, is allow two separate PC’s to sync their contents to one folder on the My Cloud. Note however there may be problems as explained in other threads when syncing two computers to the same folder on the My Cloud using the WD Sync software.
https://community.wd.com/t/wd-sync-not-syncing-between-2-computers/141218
