Thank you for your reply. In addition to AMI’s question about the Ubuntu version: Which Proxmox version are you using? I have never worked with Proxmox, but maybe the issue is related to the Proxmox version, which uses an outdated option (“bonding_masters”) when creating an Ubuntu image?
Since I don’t have Proxmox available, I’m trying to replicate the issue without Proxmox for now. If that doesn’t lead to a solution, I will see if it’s possible to install Proxmox on a virtual machine for testing purposes.