EoP causing congestion on the router

So I have 3 Desktops connected. Two are in the same room and connected via ethernet to the router, then the third desktop is connected via EoP. We have Comcast 100/10Mbps.

The two Desktops that are connected via ethernet get the full speeds (speedtest shows 80/10Mbps) and the PC connected via EoP gets odd horrid speeds of 3/10Mbps.

If I download a game through steam on one of the PCs connect via ethernet, no issues and that uses around 8-10MBps. Pinging the router still responds in an average of <1ms and a peak of 2ms.

Now, downloading the same game on steam through the EoP PC only gets around 250-700KBps download rates, and suddenly communication to the router is horrid for all three PCs. The latency for the PCs connected via ethernet skyrockets to 30-60ms and of course surfing goes down to a crawl and we are no longer able to even run a speedtest.

Checking the EoP PC, it's not using any more bandwidth then just download. Even if it were to use the most it has of 3Mbps, it shouldn't affect the router at all. If the EoP is not using any bandwidth, there is no spike in latency. As soon as it is being used, then the latency spikes. I have moved the EoP PC and conencted it directly via ethernet and there is no issue doing the same thing.

Seems that the EoP is somehow causing this issue but I have no idea what that could be or how to resolve it. The EoP has worked fine for the last year as well and this is just a recent issue that has come up.