There’s no proof they weren’t. Last report I saw on this, US admitted issues with their navigational equipment... so unless you have evidence to the contrary, that’s where things are.
I doubt that statement is true, probably just another Obama excuse. How likely is it that not one, but two state of the art Navy combat boats couldn't figure out where they were? Just how did both of their GPS navigation systems fail? And are we really supposed to believe that the US military and intelligence operations can't locate a good sized boat operating in the Straits of Hormuz, or the Persian Sea?
If the navigation systems failed on both boats then we really have to ask what happened to our military - and promptly provide every navy ship and boat with a Garmin GPS and some maps.