I wonder what your face count has become? Is it becoming too much for your computer?
Tip for narrowing down the issue (might not solve it):
What happens if you try applying a remiss of the sculpt (ctrl+r hotkey or look at the remesh tool in the header on the sculpt workspace in blender 2.8)? I would make a copy of your file and give that a go. You can turn the remesh resolution to something really high.
I heard a comment about sculpt mode bogging down under certain scenarios in theFundamentals of Sculpting video and I believe @theluthier mentioned that the remesh simplifies the sculpt in a way and does a kind-of “reset” when it gets cumbersome.
