Bigger chunks of data wouldn't upload

Hi, i am totally new to Nextcloud. I am running Nextcloud on a Windows maschine in a VM (Virtual Box). I use the 40GB version from Hansson IT.
I have expanded my storage with these two methods to 3TB:

  1. Resize virtual harddrive with CMD command
  2. Expand zfs storage (how2itsec: Increase disk and zfs of nextcloud vm running on proxmox)

Two physical harddrives are merged together through windows. They contain the virtual harddrives including the VM.

Now my problem:

Nextcloud itself works fine. Nextcloud detects the 3TB of stoarge. Web Interface works fine. Single file upload works fine too.

But when I want to upload for example a folder with pictures it works fine for like 2min and then the hole server crashes. I get an error message like this: “Error when assembling chunks status code 0”. After that the server isn’t responding anymore. It shuts itself completely off. I have to physically restart the server (windows). Same problem when using the Nextcloud app on windows pc. (Sync option)

Any idea what that could be?
Thanks for your time and help!

Best regards,

Actually found the problem. It was a hardware problem😅overheating CPU