Just want to share as it's as crazy as it might sound. My Le Max 2 x829 fingerprint miraculously came back from the dead after using the phone for the past 3 years without it. It stopped working since the 4th day after using for the first time back in 2016.
At that time, I searched these forums for solutions as it would be troublesome to ask for refund by returning the phone to China (Gearbest). I ended up using Small Eui Rom since then, but still the fingerprint didn't work. I just thought it was a hardware defect and didn't bother to install different kind of roms to revive it as the results posted here by members were inconsistent.
Then now, when I was about to retire this phone, I looked for some PIE Roms here to try new features of the Android 9.0 as the Small Eui Rom was just stuck at Marshmallow.
I upgraded my TWRP to the latest version for this phone and decided to install Revenge OS Pasta 2.5 Official Rom. I followed their instructions to flash from TWRP and added the 26S zip modem file in the process. Everything went smoothly, and I liked the rom very much and it worked fantastic, even the IR blaster worked flawlessly with the remote app from this rom. But, still no sign of fingerprint revival at that time.
Then, I searched these forums again if there's an updated solution for this old problem. I found a thread mentioned using 446D modem file and suggested that the phone should not be rebooted after installation, but instead shut it down. So, I followed the step and wait for few minutes before turning on the phone again. To my disappointment, it didn't work. The fingerprint was still dead. I didn't install any apps other then ones included in the rom and i didn't even register my Google account.
So, I just turned it off again and charged it overnight. The following evening I decided to turn on the phone again to try adding finger again, and to my surprise, the fingerprint sensor vibrated again for the first time in 3 years! Unfortunately, it failed to register a finger before time out as it could only vibrate 2 times in a row. I rebooted the phone again a few times, but it went silent again as nothing happens when trying to add a finger.
I just shut it down again and left on my desk without charging as the battery still around 76% after a few reboot attempts.
I left it for about 3 days without touching it, until one evening I decided to turn it on again. To my big survive, the long thought dead fingerprint sensor miraculously came back to life! At first, it worked sluggishly as it took a long time to register a finger, but at least it could complete the process for a finger. Fortunately, it performed better for the subsequent 2 fingers. On the 4th finger added, the registration process went smoothly!
However, after the finger registration process were done, the unlocking process were inconsistent as it sometimes worked, but failed most of the time. So, I just turned it off again.
The next day, after turning the phone on and waited a few minutes before using the scanner, the unlocking process were much better as it read faster and faster. And now, it just worked again like it never died! Yes there were still some time it was unresponsive, but it unlocked quite fast when it worked.
Maybe my experience could be useful for anyone who wants to try. I just overwhelmed this could happen!