I’m actually posting this as an answer to a problem I was unable to find a fix for anywhere online and with no obvious solutions, I was pretty much at a loss of what to do.
The Problem.
When installing -OR- updating Visual Studio 2017 you get greeted with the “Unable to download installation files. Check your internet connection and try again.” error. The other fixes that you should try are manually installing the certificates and the other fixes that are listed everywhere else online so do try those first as they are more common. You may find doing this has not fixed your problem, your frustrations at this point are probably reaching “about to snap keyboard in half” levels. Try this because this is what fixed it for me…
The Permanent Solution.
1: Fire up run, type “gpedit.msc”
2: Brows to the following location: “Computer Configuration>Administrative Templates>System>Internet Communication Management>Internet Communication settings” then find the entry “Turn off Automatic Root Certificates Update” and open her up and set it to “Disabled”.
3: Get Windows to check for updates, it will appear to do nothing (unless of course you need to actually need download updates, in which case you’ll have to update, sorry!).
4: Now try running the installer again, this fixed the issue completely and allowed Visual Studio to install without any warnings or issues.
The Other Bandaid Solution.
1: Download the build tools only for Visual Studio 2017.
2: install as necessary.
3: Once installed, open the installer and then ‘add’ visual studio to your setup.
4: This will complete with warnings but is enough to get Unreal Engine compiled.
5: If you have to update Visual Studio (which you sometimes do to get Unreal to compile if they are using a newer version) you’ll be out of luck and need to completely wipe Visual Studio from your PC and repeat the above process, it’s a bandaid solution but it’ll get you up and running if you are in a pinch.