Using VS 2017 15.5.6 and I'm seeing two separate issues with Add-in development:
Failure to deploy the App with the message:
Install SharePoint Add-in: The system cannot find the file specified.
However, the App package is successfully deployed. Re-running the Deployment step succeeds.
VS locks up during F5 debugging of an Add-in (SharePoint or provider hosted). These same lockups do not occur with a CSOM-based Windows Service running as a console application.
For the second issue, I've already run devenv /resetsettings with no improvement.