Hello Duncan,
I am facing the same issue faced by Sandeep Kumar. Earlier all my projects were built using MSBuild command line tools and the sonarqube analysis would work perfectly fine.
But now we have started to use devenv.com (located at C:/Program Files (x86)/Microsoft Visual Studio/2019/Professional/Common7/IDE/devenv.com). It gives the error " SonarQube MSBuild integration failed: SonarQube was unable to collect the required information about your projects." with possible causes as you have mentioned.
I am using Sonarqube Scanner version 5.3.1 for my C# projects.
Is Devenv.com (Commandline switch ) is not supported ?
Thanks