FreeCAD also has both Netgen and Gmsh for tetrahedral meshes and sometimes one handles the model better while sometimes the other one is superior so it’s good to have a choice. Netgen seems to be somewhat picky at times (in PrePoMax, it also fails to generate the mesh sometimes if max element size is too high) but I’ve seen a few issues with Gmsh implementation in FreeCAD too. However, it doesn’t have to be a fault of Gmsh only.
It should work: Version 1.5.0 - additional local mesh refinement? - #10 by Matej