Since Samsung uses ultra sonic sound finger print your Traces of fingerprint print can get scanned. so cleaning your traces might help. (thats why the problem with the screen guards)
also use 2 fingerprint registrations for one finger that is register one finger into 2 slots of fingerprint.
Samsung ultra sonic might be slow but it is best secured in- display fingerprint sensor available on the market.
Please be assured and perform the following steps to resolve the "fingerprint" issue:
1)To improve recognition performance, register fingerprints of the hand used most often to perform tasks on the device. 2)Ensure that the screen protector or the touchscreen on the fingerprint recognition sensor area is not scratched or damaged by objects, such as coins, keys,pens,and necklaces. 3)Ensure that your fingers are clean and dry. It should not be wet.
If the issue still persist, kindly register your concern in Samsung Members app (Samsung Members app > Get help > Feedback > Error report/ask question). Note: Please send device log files within 15 minutes of issue occurrence along with the exact issue details.
