I have not seen the wisc itself. I was curious when DS took the wisc and read "Essentials of WISC assessment" which offered a lot of insight into the test, and into uneven profiles. The sample question was online somewhere, can't recall where. Another sample question (which is likely made up, not from the real test) I saw was, "why should you tell the truth?"
Comprehension is one of the subtests that offers points for answer completeness. Vocabulary is another. It makes me feel like a tester who says, "can you tell me more", if they don't have a good rapport with the child or they say their query phrase in the wrong tone or while looking the other direction, it's possible for that to affect how much more the child feels like offering up, especially for the younger kids or those who may not really care minute to minute about the points aspect.
The use of the term "comprehension" for that subtest is pretty different from a more common educational use of the word, which might more be whether one can distill a story or line of thought to its essential parts.
You had also mentioned a low score on coding. My DS had this also, similar number, 8 or 9, can't recall. I think of coding and symbol search as "output speed". DSs slowness really affects his school experience: he experiences frustration at getting his thoughts down on paper no matter the subject matter.
