I've encountered this problem which relates to carrying the phone in a pocket: it doesn't do a good job keeping phone locked when it's in your pocket

1. Fingerprint sensor doesn't turn off when phone is in your pocket and when the screen is turned off (or it's in AOD mode) - you can unlock the phone when it's on the table face down, or by putting your hand in the pocket without intent to unlock the phone (FPR is very conveniently placed on the side of the phone, no joke, but it's the side effect - you can trigger it even while putting your phone in a pocket).
   Sony could turn it off when the screen is turned off or when proximity sensor says "it's pocket" and turn it on when user actually presses the button (before buying the phone I thought it actually works like that). If it breaks experience of fast unlock, Sony could make it an option in settings. 
2. Default unwanted actions prevention alert dialog (which I guess comes from AOSP) works bad:
   • It appears from time to time, but not every time proximity sensor is covered
   • It doesn't appear immediately on unwanted tap, meaning that if your pocket is fast enough (sweaty laps can generate multiple touches everywhere in a moment), it can do something before this dialog appears.
     What makes this point worse is that when the phone is unlocked by trust agent (like Smart Lock), it just needs to touch the lock icon on the bottom to unlock the phone.
   • Unlock panel and notifications panel can appear on top of this dialog unprotected
   • Pocket can touch OK on this dialog and it will not appear again until next proximity switch. In some cases you don't even need that - wake up screen right after turning off on this dialog or keep proximity sensor closed when you lock the phone and after that (lock phone near pocket) - the dialog can fail to appear
   The good implementation of this feature I've seen for example on MIUI 5 or 7 custom ROM I guess - lockscreen app just blocked any touches while proximity sensor is covered and showed position of this sensor so you know where to clean it and instructions in case it's broken (press power and up button for a second, I guess) on tap. I wouldn't wonder if other phone manifacturers made their own implementation, because default is..bruh
3. This one is trickier - when phone rings (Phone or Skype app), it doesn't protect screen at all - you can press all you want while closing the sensor. Tbh, I don't know how hard is this to fix, since they are apps that display "on top of" lock screen, but that's still worrying at least.