I did a new install of NCrunch and was able to uses it for a few hours. However after restarting VS NCrunch does not run. The menu items are enabled, but when I open the Tests window there are no test and the engine is not running. I am using VS enterprise 2019 with Resharper, CodeMaid and Specflow extensions.

After uninstalling NCrunch, removing all NCrunch files in my solution, rebooting, reinstalling NCrunch and opening my solution I get a dialog with "Last Chosen Setting". NCrunch is leaving files on my system after uninstall (very bad!). If I need to remove these files where are they?

I've just found a bug report submitted with symptoms similar to what you've just described (I'm I guessing this was from you). The exception encountered in NCrunch is below:

System.TypeInitializationException: The type initializer for 'nCrunch.Common.IO.PathHelper' threw an exception. ---> System.IO.IOException: The path 'C:\Program Files (x86)\Microsoft Visual Studio\2019\BuildTools"' could not be processed because it is not of legal form
at nCrunch.Common.IO.DiskPath..ctor(String absolutePath, Boolean pathIsChecked)
at nCrunch.Common.IO.DirectoryPath.FromAbsolutePath(String absoluteFilePath)
at nCrunch.Common.VsInstallationFinder.GetVSInstallPath(VisualStudioVersion vsVersion)
at nCrunch.Common.IO.PathHelper..cctor()
--- End of inner exception stack trace ---
at nCrunch.Common.IO.PathHelper.MakeAbsolutePathRelative(String absolutePathToMakeRelative, String relativeToAbsoluteDir)
at nCrunch.Common.ComponentUniqueName..ctor(FilePath projectFilePath, DirectoryPath solutionDirectory, String targetFramework)
at nCrunch.VSAddIn.Synchronisation.Solution.(FilePath , String[] )
at nCrunch.VSAddIn.Synchronisation.Solution.(DteSolutionOpenedEvent )

The system is failing when trying to find the installation of VS. I think this is caused by a malformed environment variable on your system. Can you check if NCrunchVSInstallPath.VS2019 is set to a valid path? Maybe clear this variable if it exists.