Slow Internet when connected to ethernet

[TeroFray]

I have gigabit connection. One morning I turned on my computer and noticed youtube buffering very slow. It was working perfectly the night before. Noticed stuff connected to wifi started to slow down, so I contacted costumer support, got a new modem/router sent to me.

Wifi connections are working just fine but when I connected my desktop to ethernet, it still ran slow. I haven't downloaded any new program so I dont think its a program thats messing with connection. I don't think its the main cable because when I connect it directly to my desktop, it runs perfectly but as soon as i plug it back into the wifi, my desktop slows down.  I have tried connecting my laptop to ethernet and it seems to work just fine. 

When I turn on a VPN, my internet seems to work perfectly. Anyone have ideas what could be happening? If need more info I am will provide.

[dexman]

What is the make & model of the desktop? Did it receive any updates overnight? There is another report of slow Ethernet connection speeds that has similar symptoms and now I'm starting to wonder if the computers themselves have something to do with the problem. 🤔

[dexman]

Another question just popped into my mind.....Are you on IP6 now, or still on IP4? 🤔

IP4 and IP6 Status