Yes, the mesh caused my ZBrush to crash also when I tried to subdivide it.
Here is your fixed hand back. To fix it, I first did a mesh integrity check and ZBrush found 96 out of bounds vertices. Then I clicked Fix Mesh. It fixed the mesh but it needed cleaning up as there was added screwed up geo. I seperated the fingernails from the hand and it was just a matter of hiding the good poly’s and deleting the bad. Plus, holes had to be closed in the fingernails as a result of getting rid of the bad geo. The holes were on the underneath of the fingernails. I had no problem subdividing after I fixed it so you should be good to go.
BTW…You can merge subtools and retain the subdivision levels but each subtool has to have the same amount of subdivision levels to work.
This is what the mesh looked like before I cleaned it up.
