Is your fingerprint reader on the back of the phone working fine, but after you install a case on your phone, the number of retries needed to unlock the phone increases? There is a reasonable reason why this happens and a simple way to solve, or at least improve upon this problem!
Why does it happen?
When you add a case to the phone, you are changing the “geography” of the fingerprint reader area. Your finger has to approach the reader from a different angle, and the area is further limited by the space of the case.
How to make it better?
There is a simple way to improve the readability. Scan your finger(s) again with the case on. Do not delete the old fingerprints. Just scan additional fingers with the case on, and do so as you hold the phone normally.
The fingerprint reader will then be trained to expect your fingerprints to come at these new angles forced by the phone case.