The CreateAppHost task failed unexpectedly. MSB4018

When I try and build my ASP.NET Core project, I continue to get this error message in Visual Studio 2019.
When I build it the second time, the error disappears.

Does anyone know what this error means and how to get rid of it?

Thanks!

<CreateAppHost AppHostSourcePath="$(AppHostSourcePath)"
                   AppHostDestinationPath="$(AppHostIntermediatePath)"
                   AppBinaryName="$(AssemblyName)$(TargetExt)"
                   IntermediateAssembly="@(IntermediateAssembly->'%(FullPath)')"
                   WindowsGraphicalUserInterface="$(_UseWindowsGraphicalUserInterface)"
                   Retries="$(CopyRetryCount)"
                   RetryDelayMilliseconds="$(CopyRetryDelayMilliseconds)"
                   />