Selecting Visual Studio 2017 as the preferred Source Code Editor in the Editor Preferences window only sets that preference for the current project, instead of making it a setting for any project using that Editor. Once the preferred Source Code Editor is set in a project, the following is added to the DefaultEditorPerProjectUserSettings.ini file in the project's Config folder:
[/Script/SourceCodeAccess.SourceCodeAccessSettings] PreferredAccessor=VisualStudio2017
It would be expected that this would instead be added to the Editor's EditorPerProjectUserSettings.ini file located in Engine\Saved\Config\Windows so the setting would be available for all projects using that Editor.
Note: This was tested on a machine that has both VS 2015 and VS 2017 installed.
RESULT:
The solution for the new code project opens in Visual Studio 2015.
EXPECTED:
The solution for the new code project opens in Visual Studio 2017.
Head over to the existing Questions & Answers thread and let us know what's up.