The fingerprint sensor on my G4 plus has just failed after 4 years.
For a while I assumed it was the destruction I'd wrought on my delicate digits by exchanging my desk job for manly work, but it won't even let me register a different print.
No doubt it might recover if I did a factory reset, but last time I did that, I trashed my SD card ...
I am also loathe to actually attempt top fix it because coincidentally, my phantom screen touches seem to have gone - I had the screen replaced under warranty when I first had it, but then it started going nuts again and ever since I've had to perform an annoying tapping ritual ever since every time I woke it from sleep to use it.
So I assume the screen touch-sensing is part of the same bit of hardware or firmware that handles the fingerprint sensor.