Do you have anything Bluetooth connecting to it? Headphones? I had a very interesting case where I was using my Bluetooth headphones with it and then turned it to sleep, put it in the case, and put my earbuds in their charging case. 10 mins later I took out the earbuds to use with my phone and they connected to my deck and I think it woke it up! As I was hearing my game sound, I swear I put it to sleep.
This was a concern to me as it was zipped up in the case so generating heat with no ventilation - not good.
I wonder if the Bluetooth controller wake also allows Bluetooth headphone wake in error, which I've never seen before. Hopefully not but can't say for sure, and can't test now as it's going back to valve.