Proxmox: Bridge port enp1s0 does not exist

I was adding a new NVMe drive to a previously unused slot on my little home server running Proxmox. After putting it back together, my services, like Home Assistant and Pihole, never came back online.

Running systemctl status networking, I could see the error message:

error: vmbr0: bridge port enp1s0 does not exist

Long story short:
Adding a new drive changed the enumeration of the network interface, it is now enp2s0.

Solution:
I edited /etc/network/interfaces and changed enp1s0 to enp2s0.
Running ifup vmbr0 now ran without error and networking was working again. 🎉