Set the phone up and everything is great but double tap to wake works 1 out of every 5 times. Definitely something is wrong there.
With the Sony launcher double tap to sleep works fine so I don't think this is a hardware issue.
I tested this with the stock Sony launcher and Nova enabled and both have the same issue.
This isn't my phone obviously, but this is similar to how my phone is behaving:
https://www.youtube.com/watch?v=iukYtlqDww4I tried it with the phone in my hand, and also laying flat on a table.