Here's an example.
Example? Only time I recall them being off were times when they were "supposed to be off." Unless you looking at the back of the nacelles which aren't quite as well lit as the sides of the nacelles.
And there are couple of shots like that in the episode. Even if it's the rear part of the nacelle, there is enough of it showing that the glowing blue effect should be noticeable.
Looks like a missed lighting pass.