That's usually been my issue with SJ's doing type.
They're good at details and catch small things, but often they seem to not be nearly as good at putting together the big picture.
As long as the cultural clues/behaviors they were raised with as indicative of people have not changed, they do okay; but typically out of that subculture they read things wrong. I know a lot of brilliant ISFJ/ISTJ people but they tend to misread people who are not ISTJ/ISFJ types, unless they have had extensive experience with other sorts of people that they can draw on.
There is the natural bent towards drawing conclusions based on the sign, not the underlying essence.
And the bent to draw conclusions when not enough information has yet been acquired.
And the bent to not imagine a wide enough range of possibilities for a particular behavior or see behavior in context.
That has just been my experience.
(of course, then N's go and pull the floozy "N" thing or else ignore details they don't like or even attribute too much flex in a situation where the person shouldn't be trusted to begin with, so I guess it all equals out.

)