On the Samsung Galaxy s21 Ultra In the setting on my phone I turned off the always on fingerprint so I have to wake the screen with the power button before I actually press the fingerprint sensor. The issue is(and it’s a small one but still is annoying) it throws the error that your thumb isn’t covering the whole sensor or the error to press harder before you even touch the sensor. And it’s annoying to see that every time the screen is turned on. My guess is it is reading (or attempting to read) the finger when the power button is pressed even if the finger isn’t there instead of waiting for you to actually touch it. Should be a simple software fix.
No no screen protector, I even cleaned the screen off completely and tried it. It just seems as though the signal from pressing the on button to wake the screen is prompting the sensor to read even though nothing is there even though my fingers are nowhere near the screen.
And I specifically turned off the always on fingerprint sensor so that you can't wake the screen from off without pressing the power button so nothing gets bumped as that is how I prefer it.