Proxmox Backup Server have large IOwait and becomes partly unavailable when performing sync jobs

I have setup two PBS machines (dedicated hardware with LEXAR NM610 PRO NVMEs) on different locations. Both installed with ZFS. Both machines have a similar setup

proxmox-backup: 3.2.0 (running kernel: 6.8.12-2-pve)
proxmox-backup-server: 3.2.7-1 (running version: 3.2.7)
proxmox-kernel-helper: 8.1.0
proxmox-kernel-6.8: 6.8.12-2
proxmox-kernel-6.8.12-2-pve-signed: 6.8.12-2
proxmox-kernel-6.8.12-1-pve-signed: 6.8.12-1
proxmox-kernel-6.8.4-2-pve-signed: 6.8.4-2
ifupdown2: 3.2.0-1+pmx9...

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