In the season following David's leaving the show, the show follows a case in the Utah Desert. In the Desert, an agent gets attacked and hurt. The show fades out and ends up at Brigham Young University Medical Center. The only problem is, there is no Brigham Young University Medical Center. There isn't even a medical center at that university.
I live in Boston... in the suburbs... there was an Ep. in the eight season where they were chasing the bugs in the subways... 1) They called it the "M"... it's really called the "T"... (MBTA) 2) they only did that for fictional purposes. 3) The subway system they had pictured looks absolutely nothing like it... not even the stops (WAY too clean!) They do things and make up things for reasons...
I'm from a suburb of Boston myself, and they totally changed things around. I would pay to see an area of the red line (I think it was supposed to be the red) that looked like that! Also, they combined the names of two hospitals to form the one, I think, that was actually my mother's comment. However, they do that in all episodes. There was also one in Worcester (the twin one from S8, can't recall the name) and that also was done 'incorrectly' but not through any error, it wasn't meant to be correct.
The episode that is the focus of this "slip-up" is probably Roadrunners. Scully gets attacked later towards the end of the episode.
The episode in the subway was called "Medusa" and they weren't chasing bugs. They were chasing a water-born organism that came in through a water leak in the tunnels.