Maybe running NAV and Defender simultaneously. They both might be running separate scans.
Before my new HP 400-2 24 Slim Line went back to the store I had triple layered AV Protection with adding, in order, the free version of Comodo followed by Ad-Awarer, also free copy, and chose to run it as a second layer on the install. Then, using Edge, I downloaded and installed Firefox and Chrome.
I waited until all my scans were finished and the first thing I noticed after the scans and Comodo removing a couple of discovered threats was the increase, very noticeable, in the speed of Edge. And I learned and had to redo but on install with Comodo (I discovered this system for Linux and was pleased to find it for windoze) the option to install Chrome and even if Chrome is installed, this should be allowed.
With the install through the install of Comodo Chrome is changed to Chromodo and the browser is an active AV and additional Firewall with no noticed loose of speed. I ran the tests to the same web sites from my Home Page on both versions. For anyone running any Linux flavor, this is a very minor issue but running windoze, this is a major issue and will remain so until MS moves forward, abandoning the past and dumps the Registry and ceases to add to the MS Kernel but leaving all of the past holes and other troubles resident there.
If the Redmond Team will just adopt the 'Nix model of the kernel 90% of the Virus, Worm and Trojan attacks would be over. But, as Mary Jo Foley points out, their mind set is lost in the past.