Let me see if I can explain this correctly.
This issue just happened to me. I have been having DSL issues with CenturyLink (yes I know but my MIL needed a phone). After numerous tickets and techs a knowledgeable tech came out and told me that my lines were echoing with each other because of the way my house was wired. (Basically the phone lines come into my house to one outlet and then spliced from there to the other ones.)
So he bypassed all the other outlets and just left the one I use connected to the internet. One of the tell tale signs was my router kept restarting when the internet had heavy use. It was frustrating but now my internet with Century Link ( I know I know) works wonderfully. BTW, I had three modems given to me each month thinking this was the issue and they all restarted.
So call your Internet provider and see if this is your issue.
Also, I had the same issue with my cable internet service and they did the same thing Century Link did. Go figure. new house messed up wiring.