I have the same problem with a Virtualized OPNSense under Proxmox.
What I have also found is that if I run speedtest-cli from the OPNSense VM I get a normal download speed.
Edit: I also have VLANs on the WAN side
What I have also found is that if I run speedtest-cli from the OPNSense VM I get a normal download speed.
Edit: I also have VLANs on the WAN side