Xiaomi Mi5 Fingerprint not recognised

I have a Xiaomi Mi5 with Oreo (MIUI Global Stable 10.2.2) and have a major problem with the fingerprint unlock function. I have no problem saving my fingerprints to the phone in the Lockscreen Settings. Usually I am able to unlock the phone and those apps requiring my fingerprints straight away. However after a short period the scan recognises my prints about only about 10%of the time. I am therefore dependent on the PIN. I have taken the usual steps, deleting and re-entering my fingerprints, turning off the screen lock and then setting up the PIN again and once more enrolling my fingerprints, wiping the device's cache. I have tried different fingers I have even factory reset the device.

This problem began about 2 weeks ago. Previous to that I used it for several months without a major problem with the fingerprint scanner (about 90% success rate). I do not believe this problem is due to dirty, wet or scarred fingers. The Home button (the scanner is in the Home button) looks undamaged. I did a hardware test which gave the scanner a pass. Attached are screenshots for the test.

I have looked on the web and the only possible solutions are flashing a new ROM or involve coding amendments. I am not comfortable with any of these.

I should point out there has been no MIUI version update for several months. Also I have had this problem with other Xiaomi phones - the fingerprint unlock works fine for a while then breaks down and after a while weeks perhaps will start working again. This was not so important as I seldom used those phones. However the Mi5 is my regular everyday phone and I need the fingerprint unlock to work.

I would appreciate any advice that would help.

Is it cold where you are? In the winter, our fingers actually shrivel a bit (if you have heat, that dries the air - if not, you're in cold air), and that messes up fingerprint scanners, sometimes to the point of not even being able to save new ones. Let a finger soak in warm (75°F/24°C) water for about 5 minutes, then dry it off and try again, to see if that's the problem. (I had 4 replacements sent to me by Google the first winter I had my Pixel 2 - the 4th one was brand new, but checked for fingerprint sensor working before shipment to me - it failed too. I got to the point that I asked the CS rep if they could replace my fingers under warranty. Jokingly, but that gave me the idea that it was my fingers, and I proved that it was. When the weather warmed up, the scanner started working again.)

Thanks for your reply.

I doubt that temperature is the problem. It's between a minimum 10 or 12 Celsius and a maximum 25 over here. In the house at night it would be warmer (about 15-20).

Also there is the fact that straight after setting my fingerprints it works well for a short period but then fails.

Any other suggestions from you or others would be welcome

Originally Posted by pjtwyman

Thanks for your reply.

I doubt that temperature is the problem. It's between a minimum 10 or 12 Celsius and a maximum 25 over here. In the house at night it would be warmer (about 15-20).

Also there is the fact that straight after setting my fingerprints it works well for a short period but then fails.

Any other suggestions from you or others would be welcome

Can monitor for little bit in safe mode and see if issue there

I cannot get into Xiaomi safe mode. The directions I found on the Web don't work so I have emailed Xiaomi Support for advice on Mi5 Safe Mode. I am not optimistic about any reply.