kUBUNTU: NO Persistence

[VentoyMic]

I have no success to get persistence for some actual UBUNTU-based distribution. The USB-Stick was created with ventoy 1.0.14 from an kUBUNTU (18.04)-PC.

The .json-Syntax (ref. below) was checked and after booting the stick, F5 Debug > Persistince reports OK. Booting kUBUNTU or KDEneon from the stick, I'm asked about using persistence and I agree. The systems start and I apply some modifications on the desktop (arrangement of icons, clock settings).
I shut the system down and restart it from the stick, again I'm asked about using persistence and I agree: But all modifications are gone, no persistence.

This is the structure of my USB-Stick (first partition):
./ventoy:
gParted-live-1.1.0-1-amd64.iso
KDEneon-user-20200625-1119.iso
kUBUNTU-20.04-desktop-amd64.iso
Manjaro-kde-20.0.3-200606-linux56.iso
ventoy

./ventoy/ventoy:
KDEneon20200625.img
kUBUNTU200400.img
Manjaro2003.img
ventoy.json

This is my .json:
{
  "persistence":[
      {
            "image": "/KDEneon-user-20200625-1119.iso",
            "backend": "/ventoy/KDEneon20200625.img"
      },
      {
            "image": "/kUBUNTU-20.04-desktop-amd64.iso",
            "backend": "/ventoy/kUBUNTU200400.img"
      },
      {
            "image": "/Manjaro-kde-20.0.3-200606-linux56.iso",
            "backend": "/ventoy/Manjaro2003.img"
      }
  ]
}

How to solve this?
Thank you, Michael