When I append a subtool it gets appended and is in the subtool list but I can’t really see it and there is nothing in the little preview either. All the stats are there but nothing that can be seen visually.
I thought that maybe it was a size issue and tried to center the subtool but nothing shows up.
This is in the lastest release 3.2.
it may still be a size issue, instead of using deform size, try the unify button in the deformation palette.