I have also not experienced this problem, but maybe I'm not using my phone in the same way as those who are. I very rarely let battery go below 20% and most of the time it's above 40%. I can reboot without losing prints, hard reboots (holding down power and vol) and safe mode reboots are also fine. Note that I did not update to Android 9 until it got to 5.150.
My Nokia 8 was updated from Oreo to Pie when it became available and is now on the latest 5.150 - No issues with missing fingerprint here during my normal use of the phone, including reboots and soft resets.
Maybe it's a deliberate security and integrity thing since Pie? Stored fingerprints are recognised if the phone is recharged to more than 20% before use after it has done a low power shutdown, according to others in the forum.
I'm unable to replicate the missing fingerprint issue on my phone.
Test scenario and result: At 15% power, play some Youtube videos for ~30 minutes to drain the battery until 5% remaining power. Next, take some pictures and browse the Internet until 3% left. Call the dentist and make an appointment, enter the appointment in the calendar. Leave the screen on until the phone shut itself down. Plug in the wall charger. Let it sit for a minute or two until the recharge icon shows 2% power. Start up the phone, enter the SIM PIN when prompted, tap the fingerprint reader, enter the phone PIN when prompted as usual after a restart. Lock the phone, and fingerprint unlock works as usual at less than 5% charge.
There's no further trust agents and unlock methods defined on my phone, just the SIM and phone PINs and one fingerprint. The Google app is disabled, but it's set up with a Google account and with location, mobile data, WiFi, Bluetooth etc. always on, if that matters.
Dial *#*#372733#*#* for the Android FQC self test menu. In the Battery Information Test on my phone the Battery health is Good and the battery voltage is 3600-3700mV at 3-5% remaining power. It probably shuts off around 3500mV (which is plenty to shut off clean).
On Nokia Symbian phones I'm used to get a handful of 'boing' audible notifications and an on-screen notification that the phone is going to shut down now.
For the developers to maybe consider:
* Nokia 8 with Android Pie does its regular low-power shutdown without visual or audible notifications - there is no way for the user to know if the phone shuts down clean or dirty. * /vendor/app/PowerOffAlarm system app version 9 is installed and active - but it has never sent any notifications on my TA-1012 hardware version 3.1
<blockquote class="Quote">
<div class="QuoteAuthor"><a href="/profile/jdan">jdan</a> said:</div>
<div class="QuoteText"><div>Workaround: see this comment</div><div>https://community.phones.nokia.com/discussion/comment/107934/#Comment_107934
</div></div>
</blockquote>
This doesn't help. I'm able to add the fingerprints back but that's not the point.
The fingerprints shouldn't disappear and the user shouldn't need to be adding them back. Other android phones don't need such a thing. Fingerprints must be working all the time unless the user performs a factory reset.
<blockquote class="Quote">
<div class="QuoteAuthor"><a href="/profile/user389">user389</a> said:</div>
<div class="QuoteText"><div>@Jivko Antonov and others,</div><div>I'm unable to replicate the missing fingerprint issue on my phone.</div><div>Test scenario and result:
At 15% power, play some Youtube videos for ~30 minutes to drain the battery until 5% remaining power. Next, take some pictures and browse the Internet until 3% left. Call the dentist and make an appointment, enter the appointment in the calendar. Leave the screen on until the phone shut itself down.
Plug in the wall charger. Let it sit for a minute or two until the recharge icon shows 2% power. Start up the phone, enter the SIM PIN when prompted, tap the fingerprint reader, enter the phone PIN when prompted as usual after a restart.
Lock the phone, and fingerprint unlock works as usual at less than 5% charge.</div><div>There's no further trust agents and unlock methods defined on my phone, just the SIM and phone PINs and one fingerprint. The Google app is disabled, but it's set up with a Google account and with location, mobile data, WiFi, Bluetooth etc. always on, if that matters.
</div><div>Dial <b>*#*#372733#*#*</b> for the Android FQC self test menu. In the Battery Information Test on my phone the Battery health is <b>Good</b> and the battery voltage is <b>3600-3700mV</b> at 3-5% remaining power. It probably shuts off around 3500mV (which is plenty to shut off clean).
</div><div>On Nokia Symbian phones I'm used to get a handful of 'boing' audible notifications and an on-screen notification that the phone is going to shut down now.</div><div>For the developers to maybe consider:
</div><div>* Nokia 8 with Android Pie does its regular low-power shutdown without visual or audible notifications - there is no way for the user to know if the phone shuts down clean or dirty.
* /vendor/app/PowerOffAlarm system app version 9 is installed and active - but it has never sent any notifications on my TA-1012 hardware version 3.1</div><div>--
Hans
</div></div>
</blockquote>
Just restart the phone, it flushes the fingerprints.
Comments
Stored fingerprints are recognised if the phone is recharged to more than 20% before use after it has done a low power shutdown, according to others in the forum.
Hans
At 15% power, play some Youtube videos for ~30 minutes to drain the battery until 5% remaining power. Next, take some pictures and browse the Internet until 3% left. Call the dentist and make an appointment, enter the appointment in the calendar. Leave the screen on until the phone shut itself down.
Plug in the wall charger. Let it sit for a minute or two until the recharge icon shows 2% power. Start up the phone, enter the SIM PIN when prompted, tap the fingerprint reader, enter the phone PIN when prompted as usual after a restart.
Lock the phone, and fingerprint unlock works as usual at less than 5% charge.
* /vendor/app/PowerOffAlarm system app version 9 is installed and active - but it has never sent any notifications on my TA-1012 hardware version 3.1
Hans
Thanks
<div class="QuoteAuthor"><a href="/profile/jdan">jdan</a> said:</div>
<div class="QuoteText"><div>Workaround: see this comment</div><div>https://community.phones.nokia.com/discussion/comment/107934/#Comment_107934
</div></div>
</blockquote>
This doesn't help. I'm able to add the fingerprints back but that's not the point.
The fingerprints shouldn't disappear and the user shouldn't need to be adding them back. Other android phones don't need such a thing. Fingerprints must be working all the time unless the user performs a factory reset.
<div class="QuoteAuthor"><a href="/profile/user389">user389</a> said:</div>
<div class="QuoteText"><div>@Jivko Antonov and others,</div><div>I'm unable to replicate the missing fingerprint issue on my phone.</div><div>Test scenario and result:
At 15% power, play some Youtube videos for ~30 minutes to drain the battery until 5% remaining power. Next, take some pictures and browse the Internet until 3% left. Call the dentist and make an appointment, enter the appointment in the calendar. Leave the screen on until the phone shut itself down.
Plug in the wall charger. Let it sit for a minute or two until the recharge icon shows 2% power. Start up the phone, enter the SIM PIN when prompted, tap the fingerprint reader, enter the phone PIN when prompted as usual after a restart.
Lock the phone, and fingerprint unlock works as usual at less than 5% charge.</div><div>There's no further trust agents and unlock methods defined on my phone, just the SIM and phone PINs and one fingerprint. The Google app is disabled, but it's set up with a Google account and with location, mobile data, WiFi, Bluetooth etc. always on, if that matters.
</div><div>Dial <b>*#*#372733#*#*</b> for the Android FQC self test menu. In the Battery Information Test on my phone the Battery health is <b>Good</b> and the battery voltage is <b>3600-3700mV</b> at 3-5% remaining power. It probably shuts off around 3500mV (which is plenty to shut off clean).
</div><div>On Nokia Symbian phones I'm used to get a handful of 'boing' audible notifications and an on-screen notification that the phone is going to shut down now.</div><div>For the developers to maybe consider:
</div><div>* Nokia 8 with Android Pie does its regular low-power shutdown without visual or audible notifications - there is no way for the user to know if the phone shuts down clean or dirty.
* /vendor/app/PowerOffAlarm system app version 9 is installed and active - but it has never sent any notifications on my TA-1012 hardware version 3.1</div><div>--
Hans
</div></div>
</blockquote>
Just restart the phone, it flushes the fingerprints.
After charging and restarting I could add the prints back - but not before
very annoying