Feces (stool) floats because of an increased content of gas or water (or both).
This question was addressed in a prestigious medical journal, the New England Journal of Medicine (May 4, 1972) by Dr. Michael Levitt from the University of Minnesota, who is an authority on intestinal "gas."
To float, stools must contain gas. Whether the stool is a "floater" or a "sinker" depends upon differences in gas rather than fat content. A high stool gas content (and hence a floating stool) is related to gas (methane) content.
Thus, stools float because of an increased content of gas or water (or both). There is nothing wrong with "floaters."