BCAAs have a slight stimulant effect on me, but only when I'm carb depleted. It's very subtle but I find it gives a slight boost of energy and helps me to focus on tasks.
I often take pure BCAAs right before bed, they seem to help me sleep and can often give very lucid dreams.
As mentioned, some BCAA formulations contain caffeine, or copious amounts of B-vitamins - both which can affect sleep, but neither of which seem to be in the formulation you're taking.
Don't know what to tell you - I guess everyone responds differently to things