You can google "disable killer network service" and look at the instructions on Intel's site. The second part (marked "Optional") matches what I did on my machine (the first part doesn't apply to me as I never had the Killer Control Center installed, just the services).
I had the same issue, but Safe Mode (the STO one) did not fix it, nor did any of the other suggestions in this thread. Eventually I did find the root cause (at least for me) - weirdly, it was caused by my network drivers. While trying to diagnose this thing, I noticed I had very slow upload at speedtest.net (under 1 Mbps,…