I installed Iperf on pfsense and I ran a test through one device from the LAN to the Firewall and another test through one device from the WAN to the firewall.

The results from the LAN are correct, I get around 900Mbit/s.
The results form the WAN are very poor, I get around 47Mbit/s.

On the Firewall side there's a symmetric 600Mbit/s fiber line.
On the WAN device side there's a symmetric 300Mbit/s fiber line.
The hardware running pfsense is a Super Micro XG-1537.
The CPU load is only 1%.
I ran a speed test via py37-speedtest-cli from the Firewall and I got around 585Mbit/s symmetrically.

Do you have any idea why this is happening?

Any help will be very appreciated.