It is great that your device has no issues, but some of us do have problems. And, by sharing the problems and concerns we hopefully can expedite the solution. I had the P5 and P4 and the FPS was near perfect. Not so much with my P6. There are times when it takes 4 or 5 tries, and times where it won’t open at all. I have turned off, re-booted and factory reset.
This should not happen. Something changed from the previous devices…… it needs to be addressed
Changing from a capacitive to an optical sensor necessitates a change in expectation of performance. Simply put, an optical under-display sensor is going to be slower and less reliable than a capacitive sensor. Other OEM's have moved on to ultrasonic sensors which can be almost as fast and reliable, and even more secure, than capacitive sensors, while likewise beating out optical in both respects.
If you want the speed and reliability of the capacitive sensor you had on your P4 and P5, you're pretty much out of luck with newer upper mid-range to flagship phones. Sadly, the industry is moving away from them because they lack the 'wow-check-out-how-I-can-unlock-my-phone' factor they opted for to differentiate themselves.
I don't have my P6 Pro in hand yet (should be arriving any time, knock on wood), but sight-unseen I anticipate that Google electing to use an optical scanner over the much more widely used ultrasonic scanner (or even using a capacitive sensor embedded in the power button) will be my biggest letdown with the device. But coming from a Samsung that uses an optical sensor, so long as it is a similar range of performance I won't really be that upset.