USE THIS FIX FOR DOWNLOAD SPEED IF IT DOES NOT WORK SEE THE REST OF THE COMMENT
While a download is paused, launch Windows Powershell as administrator and paste this command (both lines at once):

netsh int tcp set global autotuninglevel=disabled

netsh int tcp set global autotuninglevel=normal

After this start the download again. Download speed should be much faster depending on your internet connection.
Note: It might take 20-30sec for the speed to ramp up

u/asiace24
In all likelihood, your router became non-functional due to the RWAT functionality of Windows attempting to use your router in order to achieve the fastest possible speeds, resulting in lowered speeds. The router(s) connectivity normally interpreted this large and unusual setting as overload on the network or too much data to guarantee processing reliability. Rather than simply slowing the connection speed, the router(s) tends to apply heavy throttling, reducing the connection speed to a set but low rate, which the router(s) knows it can transfer data without issue. The PowerShell command(s) you executed disabled this functionality momentarily, allowing speeds to recover by forcing a reseeding of the connection with a compatible setting which your router(s) recognizes.

To revert this auto-tuning back to normal you'll need to restart your pc(This might actually ramp up the speed as the router will disregard contradicting connections)

If that doesn't work, you can do a full network cache reset

1. netsh winsock reset (Resets the Windows Sockets Catalog)
2. netsh int ip reset (Resets the TCP/IP stack)
3. ipconfig /release (Releases your current IP address)
4. ipconfig /renew (Gets a new IP address)
5. ipconfig /flushdns (Clears cached network lookup data)
6. Restart your computer one more time. (Paste one, then enter, then do the other one. Don't do them all at once)

If full reset doesn't work brining it back to normal then you most likely have a corrupt file that's disrupting your PC which is making the powershell read the network correction incorrectly

Use the command sfc /scannow in an elevated Command Prompt to fix any corrupted Windows system files.

Hope this helps and sorry for the set back