I spent an entire afternoon debugging a VM that refused to boot, only to find out my GPU had decided to change its PCI address. One reboot and the device that lived at 01:00.0 suddenly migrated to 02:00.0 . Because my Proxmox VM configuration was pinned to the old address, the VM crashed with a QEMU assertion error, and the GPU simply vanished from the guest. This usually happens because of how the BIOS handles PCIe enumeration during POST. If you have multiple PCIe devices or a complex motherboard topology, the bus numbering isn't always deterministic. This is compounded by AMD Ryzen C-states or weird UMA frame buffer settings that can delay device initialization, causing the kernel to assign addresses in a different order than the previous boot. If you've already dealt with AMD iGPU RAM theft , you know how sensitive these BIOS settings are. If you're on Proxmox 8.4+, the "happy path" is to use the q35 machine type. The older i440fx is more prone to these PCI mapping failures and IRQ conflicts.…