I hate to be the guy with a very specific problem that either no one has, or no one talks about... Yet here I am.
After installing a Security Update for Windows 10, my internet has begun to act oddly. The update also broke a lot of the Explorer menus, but I was able to fix that so that's likely irrelevant - though to be thorough, I'm mentioning it. Internet speeds are fine when the PC first boots, but after about 30 seconds of being on Desktop, any downloads drop to the 400-or-less kiloBYTE range. Prior to "the incident", my internet speeds were normal. I uninstalled the update and still have the same issues. I've tried about everything that I can think of that is rational.
I assumed, from the sudden drop in internet, that some app is taking up all of my bandwidth, though Task Manager reads my network at 0%, and I have killed all third-party processes that may connect to the internet. That only solved to further my frustration. I've sanity checked WiFi and Ethernet speeds on three other devices, and all other devices return "normal" theoretical and real-time speeds. The slow speeds are quarantined onto my new PC alone, and are unanimous across any and all apps that can gain internet access.
Tried:
-Powering off and unplugging Internet Modem for at least 60 seconds
-Running Windows Troubleshooter (ha!)
-Ensuring Delivery Optimization options were set for maximum download capability
-Temporarily disabling Windows Update in case of hidden or bugged file download(s)
-Reinstalling most recent MoBo LAN driver(s)
-Reinstalling most recent Wireless Adapter driver(s)
-Backdating to a previous Mobo LAN driver
-Backdating to a previous Wireless Adapter driver
-Rebooting into Safe Mode (with Networking)
-Uninstalling suspected Windows Defender Version
-Reinstalling Windows Defender Version (and future version)
-Running Windows Security Threat Scans
-Shutting down any and all 3rd party apps
-Running DISM in elevated PowerShell/Command Prompt (primarily for Explorer issues that have since been fixed)
-Running SFC in elevated PowerShell/Command Prompt(primarily for Explorer issues that have since been fixed)
-Checking for updates repeatedly
-Updating system Firmware
-Ensuring Networking drivers are not corrupted
-Updating BIOS per manufacturer's specs
-Internal Monologue
-Profusely Swearing
Have Not Tried:
-Tap Dancing
-Buying Alienware
Specs:
CPU, AMD Ryzen 7 1700
Motherboard, ASRock AB350 Pro4 (came with GPU)
GPU, ASRock Radeon RX 580 8GB Phantom Gaming X
RAM, G.Skill F4-3200C16D-16GTZB
Wireless Adapter, TP-Link AC1300
SSD, Mushkin Pilot 250GB M.2
HDD, Western Digital WD8003FFBX
Power Supply, EVGA 210-GQ-0650-V1
OS, Windows 10 Professional, 64bit, Version 18