I imported a Victoria 4 model, hit D and it turned out just fine. Couldn't reproduce your issues. Of course sculpting that high poly model was impossible to begin with (least on my machine). You probably want to look into image based sculpting. It's basically sculpting using displacement maps rather than sculpting right into the geometry. You can achieve details with this that would be impossible otherwise since you would need a far too dense mesh. Also this should get rid of your UV issue.

The modo In Focus videos have a nice intro to image based sculpting. Basically the same as sculpting geometry, just need to set up a vector displacement map first.