Try this - Settings - Three Dot Menu Top Right - Show System Apps - Search for Biometrics - Storage & Clear Cache & Data for Biometrics.
You could also try removing your Finger Prints & Register them again
I found this on the web, hope it help, i have no other solution :
Hey I had this same issue on my SM-N960U. I tried just about everything I could find online. Nothing really did it. However, I recently performed a security scan to find I had malware on my device. I removed the malware via tools on my device, cleared the cache, and restarted the phone. All the sudden it was working again. I hope this helps anyone who has come across this issue.
UPDATE: Regarding my last post, this seems to be a temporary fix. As my phone is acting up again. If this has worked for you I recommend deleting old prints and adding new ones as this may alleviate the issue further. Let me know your results. I am eager to hear others findings as this seems to be an ongoing issue for many people.
NOTE: As far as I can tell this method doesnt work a second time, so strike while the iron is hot I suppose.
I have same problem with fingerprint in my phone (note 9) _ suddenly I tried to open my phone by fingerprint but wasn't working, I tried to add another fingerprint it's also not working.
What can I do ?
I have been having the same problem with my Note 9. Mine also started about 3-4 weeks ago. I have restarted my phone several times. I have removed the previous fingerprints and added them back four times. Every time it passes all the tests and works for a while, but after a few hours it stops recognizing them again. Chatted with someone at Samsung who had me clear the cache partition and that didn't help. Has anyone found a reason for this yet and hopefully a fix? If not, it's just about as easy for me to just put in my 4 digit pass code.