Hi, I notice that salome 9.15 does not show volume element edges correct. At least my installation does not.. Some edges are missing. See figure below and the file attached.
Yes, you found a work around. But not so convenient if one wants to display both volumes and some of the face groups. Easier to use v9.14 to create pictures then. Hopefully this is fixed in next version!
you can also display face groups, i only remove everything else for make it more clean.
nevertheless obviously it should be fixed. i would recommend to make an issue in the smesh git.