Terry O'Quinn, who plays SAC Darius Machaud, dies in the bomb sequence at the beginning of the movie, yet returns in Season 9 as the Shadow Man in The X-Files: Trust No 1 (2002) - only to die again in the Magnatite quarry. He also played Lt. Brian Tillman in The X-Files: Aubrey (1995)
The young boys and the townspeople from the "North Texas/Dallas" area in the movie all talk with heavy accents. This is erroneous; the stereotypical southern drawl is present in people from West Texas, whereas inhabitants of North Texas (including the Dallas area) and East Texas do not possess discernible dialect from the average American accent.
The movie takes place in July but during the sequence in Antarctica the Sun is up (fairly high). During July, the Sun never rises in Antartica (at least not at the coordinates given by the Well Manicured Man).