I've seen this on occasion. There may have been a problem with the Avast! install. It would be interesting to see if the Windows Security Center is detecting Defender or Avast! as your AV products. Either way, I'd recommend uninstalling and reinstalling Avast!.
I'm not sure if this will help you, but try opening file explorer and going to [b]%programdata%\[/b] Browse to the Microsoft folder, and then to Windows Defender. When you first open this folder, you may get a message asking whether you want to grant access (or something along those lines). Once you grant the access to open it, Host Checker may be able to detect that Defender is turned off.
If you can't get to %programdata% you may need to toggle the setting that makes hidden folders visible.
I had to follow these steps the first time I connected to our VPN server using Windows 10 / IE11 and Windows Defender as my primary AV.