I had this problem all the time, usually down to the frame not being cleaned properly. Make sure you're using the original waterproof (supposedly) adhesive. Get some micro-clamps and clamp it down in each corner but do NOT clamp anywhere that is near the screen. I learned the hard way and did damage to a Z2 lcd, it wasn't big damage but you could see the pressure from the clamps.
So, just clean the frame with IPA or whatever you use and clean the LCD and then make sure you properly apply the adhesive without creases etc.
I personally hate working with Xperia's. I have one of my own that I've had for ages because either the LCD will come apart or the back glass will come apart, very easy to repair but so annoying to get right.
Hope this helps