This is definitely a common flaw. If I recall correctly, he gives up on endings altogether in Anathem, with the narrator literally writing something along the l

This is definitely a common flaw. If I recall correctly, he gives up on endings altogether in Anathem, with the narrator literally writing something along the lines of "there's much more left to tell, but this is enough." Seveneves skirts the issue by basically slapping together two rather disjoint stories, ending one "book" by abruptly beginning another. Not the worst flaw in an author, once you know to expect it.