Hey everyone,
I got an IMPORTANT Info for everyone! On one of my LXC Container had, for whatever reason, overlay2 as storage driver with ZFS as backend FS enabled. Why did I noticed it? Because it crashed my complete Proxmox Node!
It will crash when you make a backup. As soon as the backup starts the behaviour will happend what I asked here: [SOLVED] - Backup crashes WebUI / Promox Envoirement | Proxmox Support Forum Digging further in I noticed then the other storage driver.
My fix was to force fuse-overlayfs in /etc/docker/daemon.json
Now the backups running fine again 