Severe Download Speed Limitation on Newly Provisioned VMs and CTs (Proxmox 8.4.1)

I’m currently running Proxmox VE 8.4.1 and recently started experiencing a major issue with network throughput—though I’m not sure exactly when it began. Problem Summary:​ All newly provisioned VMs and containers (CTs) are seeing download speeds below 1 Mbps , regardless of OS or template used. Upload speeds remain near 30 to 100Mbps VM-to-VM traffic (on the same subnet and host) performs normally…