Msbuild build with sonarscanner enabled is so slow it's nearly useless

  • msbuild sonar-scanner-4.3.1
  • Building a largeish .net solution (~50 projects, 650k lines of code)
  • Build without running sonarscanner begin first takes 3-4 minutes.
  • Build with sonarscanner enabled takes 4.5 hours on my dev pc - times out after 10 hours(!) on build server

I have no idea how to debug this. Where do I start? The build log is too big to attach, but can be downloaded at