Network speeds drastically reduced overnight.

Issue:Overnight my download speeds have dropped drastically on this PC. Other devices show typical speeds of 65 Mbps down and 10 Mbps up. This PC is showing roughly 5-7 Mbps down and 10 Mbps up on 5 GHz network and around 25 down and 10 up on my 2.4 GHz network. This is consistent over multiple tests and browsers of course.

Info:

• Windows 10-1511 Build 10586.164
• No firewall/AV enabled (Windows Defender disabled in GPEdit.)
• Linksys WMP600N Wireless adapter (802.11 b/g/n Dual band).
• D-Link DIR-850L router (802.11b/g/n/ac Dual band).

What I've tried/checked so far:

• Malwarebytes turns up nothing on full system scan.
• Task Manager / Resource Monitor shows nothing is using network out of the ordinary.
• Tried 4 different WLAN driver versions with the same results no matter which is installed.
• Ran TCP/IP stack reset (netsh i i r r).
• Reset winsocks (netsh winsock reset).
• Flushed DNS.
• Restarted PC.
• Powercycled router/modem.

Attempting Ethernet would be extremely challenging and I'm 99% certain this is specific to the WLAN adapter. Any suggestions or ideas would be greatly appreciated.

I agree, it would appear to be specific to the card. A quick search shows people having similar issues. I did note one person specifically enabled 'gaming mode' in the advanced options for the driver - and set his router to fixed bandwidth (40Mhz as opposed to 20/40Mhz). Maybe that would help? Another option, which is entirely up to you - is that apparently there's a 'realtek 2860' driver that others have been using instead of the Linksys driver.

Thanks for the feedback. Didn't seem to make a difference although yesterday I started hitting around 50/10 (which is better but still 15 less down than normal) on the 2.4 GHz band, still only getting about 7 down on the 5 GHz band though. I do a lot of local streaming with this particular PC as the host so it'd be ideal to have it on the 5 GHz band. I'm still not 100% certain if this is only affecting the internet download speed or if its all network traffic that is congested on that band from this particular adapter, though as noted before other devices have no problem with down speed on the same band.

I'm totally out of ideas now.