since u have 3 option to add finger so...
1) remove all fingerprints
2) add ur right hand thumb and left hand thumb in same slot
3) leave the other 2 slots .....
4) turn off fingerprint animation....
5) go to setting optmise battery usage..> then in 2nd option their is optmise battery usage select it. >>then select to all... (se screenshot) >>>then search biometric and turn it off....
Dear Samsung Member,
Greetings from Samsung Customer Support!
Please perform the below mentioned steps to resolve the issue:
* To improve recognition performance, re-register your fingerprints.
For further assistance, register your concern in Samsung Members Application (Open Samsung Members Application > Get help > Send Feedback > Error report/Ask questions).
Thank you for writing to Samsung.
Samsung Customer Support