No Sync on LVM-HDD

If i set the Sync-Folder to a folder on a LVM-HDD (2x TB) it breaks off.
First the download starts and then it is interrupted (upper part of the image).If I restart the client, it cannot find the folder.

System: Linux Mint 18.3

NextCloud Client: 2.3.3

When I put the sync folder on the system disk everything works fine.
The normal user has read + write rights in the selected folder.