The fingerprint registration process was broken in firmware versions and . It would read the fingerprint normally until the process reached 41 percent completion. It would either require too many attempts to finish the registration or simply throw up an error that said “Make sure the fingerprint sensor is clean and dry, then try again”.
Samsung is now rolling out the December 2019 security patch for the Galaxy A50 and a handful of other devices. The update for the Galaxy A50 also fixes this issue. Those who were unable to re-register their fingerprints on the device will be able to do that once they get the latest update. The firmware version is gradually rolling out.