DrawMeshNow happens outside the usual render loop. At the point in time when it is executed, no camera is actively being rendered. As a result, camera-related data, like the projection matrix, should be treated as uninitialized data, and not be used by the shader. No guarantees are given to what camera-related shader properties are set to, and any value incidentally set should not be relied upon. The behavior of these properties can change at any point in time.
The repro project also uses GL.LoadProjectionMatrix. This function is not intended to be used together with DrawMeshNow, and only affects subsequent GL.xxx calls like GL.Begin / GL.End. Note that the use of the entire GL class is discouraged, and usually not very performant.
The recommendation to resolve the issue is to use a custom shader that does not access camera matrices for the DrawMeshNow call