@Remco, thanks for the insight, I didn't know of the limit of 3 instances.
Quote:under normal circumstances we should be able to handle up to 3 instances with the MSI
What is the definition of "instance"? If I open up the VS2019 installer, it shows 3x VS2019 (Community, Pro and Enterprise-Preview), plus 1x VS 2019 Build Tools. If that latter is considered an "instance", than the total number of instances is 4, not 3 on my machine.
Also curious: are 2017, 2019, preview/RTM releases considered separate for the counting up to "3 instances"? I also have VS 2017 (Pro, Community, Pro-Preview, Comm-Preview, Build Tools). That brings the full list of instances to 9.
Perhaps relevant: some have a given instance-nickname, others have the default from the VS installer (which is just a number).
Running vswhere.exe without "preview" option selected shows 2 instances VS2019 and 2 instances VS2017, it does not list the Build Tools. I would assume vswhere and MSI use the same API, but I'm guessing.