Ethernet either not working or slow on all equipment, but wirelessly, everything fine

Recently moved, xfinity helped set up our internet but we have our own modem (SURFboard® DOCSIS® 3.1 Cable Modem) and router (TP-Link - Deco BE5000 Dual-Band WiFi 7 Whole Home Mesh System 3-Pack - White).

The wireless connection is solid for the most part, but the big issue is that anything connecting via ethernet is either not working (ethernet is registered but not internet is coming in), or the ethernet throttles the internet to a halt. 

This issue is seen on both LG TV's we have and hard wiring my PC to the internet (thankfully my PC has wireless capabilities, otherwise I couldn't use it).

Not sure how to resolve the issue. We already had the home builders look at our ethernet ports and they verified internet was coming out of the walls.