I have the exact same issue with version 4.17.1. I’ve just uninstalled Visual Studio 2017, uninstalled Unreal Engine 4.17.1, ran the Visual Studio Total Uninstaller (GitHub - microsoft/VisualStudioUninstaller: Visual Studio Uninstallation sometimes can be unreliable and often leave out a lot of unwanted artifacts. Visual Studio Uninstaller is designed to thoroughly and reliably remove these unwanted artifacts. ), then reinstalled the whole lot.
Starting a Basic Code C++ project in Unreal, I let the project load in Unreal Editor and Visual Studio, before closing Visual Studio. I set the Source Code Editor to “Visual Studio 2017” from “Visual Studio”, then create a new C++ blank class. Visual Studio opens, although the toast saying “Loading Visual Studio 2017” in the Unreal Editor will remain on screen indefinitely. Leaving the Source Code Editor set to “Visual Studio” will make the toast function correctly when attempting to open the class from the Unreal Editor, however it creates a couple of warnings…
LogVSAccessor: Warning: Couldn't goto line number '0' in '.../Documents/Unreal Projects/MyProject/Source/MyProject/MyCharacter.h'
LogVSAccessor: Warning: Couldn't goto line number '0' in '.../Documents/Unreal Projects/MyProject/Source/MyProject/MyCharacter.cpp'