RolandBP in the Steam discussion forums kindly informed us about a bug on the route that can cause the scenario editor to show a black screen (no lighting of the environment) when trying to edit a scenario on the Kingwood Branch route.
While I do not fully understand the nature of this bug yet, it seems to be related to the weather and/or terrain texturing settings in the RouteProperties.xml and TemplateRoute blueprint. I am linking a hotfix below, containing updated versions of these two files. With them, I have not been able to get the bug to show up any more.
Please backup the two original files first before installing the hotfix.
The modified files are:
Assets\VNHRR\WVN_Railroad\TemplateRoutes\West Virgina Northern.bin
Installing this patch is not necessary if you do not want to edit or create your own scenarios.