No idea why this sometimes happens, but Unity prefs is set to use VisualStudio 2015… however when starting a new project… or just dbl clicking on a cs script from the editor after launch… It will startup VS first… but won’t load the script up, just the project.
And monodev will load up in the background, but will have 2 errors like 
However monodev does load up the script file after closing that error. Then if I close monodev and open the same script in Unity again it will open it up in the already opened VS instance…