Fix: “A numeric comparison was attempted” at VS build (Costura.Fody)
After upgrading from Visual Studio 2017 to Visual Studio 2019 I was able to update NuGet packages Fody and Costura.Fody of a solution that needed them (to package assembly DLLs inside console EXEcutables) and the solution was rebuilding fine.
However after I synced the solution via a Git repository on another machine and installed the newer Visual Studio there too, I rebuilt the solution in order to fetch/rebuild NuGet packages too and although everything seemed to rebuild fine, when I was using a plain build instead of a rebuild all I was getting at Errors dialog for each project that was using Costura.Fody:
Error
A numeric comparison was attempted on "$(MsBuildMajorVersion)" that evaluates to "" instead of a number, in condition "($(MsBuildMajorVersion) < 16)".
To fix this I had to uninstall and reinstall Costura.Fody NuGet package (it wasn’t needed to uninstall/reinstall the Fody NuGet package itself) on the solution’s projects that were using it and then all was rebuilding/building fine again on that other machine.
George Birbilis @zoomicon 
I’m seeing this problem myself, but your solution didn’t work for me. The only thing that works is building the solution exactly three times in a row. After that, any combination of Clean and Rebuild works. However, building from a fresh repository (or doing “git clean -fxd”) brings back the build errors.
Since Fody (and Costura.Fody too I think) update often, maybe you could try to update those NuGet packages in case it gets solved by itself. Have you upgraded them at all since it stated occurring?