I am having trouble importing dwgs in 2018. Sketchup invariably crashes when I try it. Once it returned a message to the effect that there were objects too far from the origin but it continued crashing even afetr that was solved.
On the other hand, the same file can be imported into 2017! I am not sure what to think of this apart from the fact that 2018 seems to be more unstable than other versions of Sketchup.