It is a closed facet body and the auto fix button does nothing. I cut off the thin sections off the end and tried auto skin again but the same problem appeared. as seen below
Could there be another way around the problem? The method in your third video seems exactly what I need as I need a fluid domain inside of a solid domain, or do you think the problems meshing with that method and the problem with auto skin are linked? What are the ways to smooth an stl file or solid model that you mention at the end of your third video?
I am very grateful for your time and help.