One of my kids had a discrepancy like that between the WISC and the WJ. His WJ cognitive scores were about 20 pts lower than his WISC scores. His WISC GAI was 143. I think that different tests suit different kids, and then there are other factors like tester rapport, how well they slept the night before, etc. I will say that this child is 2e with dyslexia, which I feel strongly also makes him an inconsistent performer.