Welcome!
First of all, you already have IQ scores that indicate that your child is likely 2e gifted/LD. In order for him to have a full scale in the average range, with visual spatial in the GT range, his other scores have to have been markedly discrepant. That doesn't take away the strength of his visual spatial skills. And his CogAT is generally consistent with the WISC-V, considering the kinds of tasks that are administered in the respective tests, and also making some small allowances for his more positive testing experience.
I'm guessing he also had a lower PSI, based on your note about IEP-mandated handwriting/OT interventions, and delays in written expression, which suggests a second reason the FSIQ might not have been the optimal estimate of his overall ability.
It still seems like a good idea to proceed with the BB 2e eval, as this round might be more accurate, based on his age, where he is behaviorally, and the better instructional match that he's experienced more recently. And a skilled clinician knows to interpret the data in the light of the whole child, and not the other way around.
