Nonplussed is also used to mean "uninspired" or "unimpressed" - like when something is perhaps a little out of the ordinary [there is an expectation that it will have an impact one way or another] but still doesn't really have an effect on; almost exclusively in the phrase "I was pretty nonplussed by it all" or a close analogue of that.

Certainly this is the usage I've heard and used for the last 20 years or so.