Ethernet limited to 100 Mbps

My gateway is getting 500Mbps, Wi-Fi devices can reach close to that speed, but my ethernet ports are locked at 100Mbps. My Windows PC has no wireless adapter, and I don't care to buy one because I shouldn't need to.

I have an XB6, both ports are Gigabit. They display flashing orange lights.

I'm using a 10' Cat5e cable, and I've tried using a different Cat5e. My motherboard has a GbE port.

Changing Speed & Duplex from Auto to 1.0 Gbps Full Duplex has no effect, other than briefly showing my link speed to be 1000Mbps in Windows settings, but when it actually connects to the network it changes to 100Mbps again.

I've done all this troubleshooting without a VPN.

I've got a headache trying to figure this out. Any help or possible solutions outside of the few I've mentioned is appreciated. Thanks in advance.