When you are actually asleep, your sleep cycle results in cortisone eventually being released to wake you up.
Intense exercise gives cortisone a momentary bump. It's quite logical that it would interfere with getting to sleep if it's in the evening..
Crossfit is needlessly intense, and therefore gives you a needlessly pronounced and prolonged cortisone bump.
Don't do crossfit.
I realize you may not like that answer.
There are other explanations for insomnia, but this one is exercise related.