[Moto Z Guides, News, & Discussion] D13H4RD2L1V3:
Just for background info, at the time it happened, my Z was running NPL25.86-30 from the following thread;

https://xdaforums.com/moto-z/development/android-nougat-moto-z-versions-t3506342

It was running perfectly fine, then an OTA thing appeared. Well, I made the single big mistake of accepting it, and thus, it encountered an error and while the phone booted fine and even displayed the new build "NPLS-25.86-30-5", it started to randomly reboot when the phone either goes to sleep or when CPU loads are very low.

Well, I was distraught. The phone which was working perfectly fine just a few minutes ago was rendered almost useless as I had to keep turning it off after I used it to avoid it going into a reboot loop. So making calls was difficult enough as the phone would never receive a call as it would be endlessly rebooting anyway.

So, when I returned home, I fired up ADB, connected the Z in Fastboot mode and reflashed the NPL25.86-30 firmware from that link. For a while, it seemed to be fine, but then it started doing it again. I tried again and it still does so.

I was at a loss as I wasn't sure what else to do. Since the OTA update was there, I was afraid that the bootloader may have upgraded and causing me to lose my downgrade. However, when I used the command "fastboot boot xxx", I noticed the Marshmallow boot screen, indicating that the old bootloader was indeed intact and it hasn't changed.

It also happens that I kept the original firmware file which my phone came out of the box with. So I fired up RSDLite, put the entire .zip file in it (including GPT and bootloader) and flashed it right away. After it was done and I did a hasty setup, I left the phone alone to see if it would do so. Over an hour passed, and the phone never rebooted by itself, and would only do so if I was the one doing it.

So, there was light at the end of this very dark tunnel. Fired up ADB yet again and flashed the NPL25.86-30 firmware using the method that does not upgrade the bootloader. I also flashed TWRP and erfanoabdi's TurboZ kernel to disable forced-encryption and dm-verity, along with phh's Superuser for root access as SuperSU somehow does not install right even though the recovery says otherwise.

Booted up and it hasn't rebooted by itself until now. The only time it has rebooted is when I did it. It did necessitate a full data reset, but so far, it has been running well, with the OTA service fully disabled and the processor clocked to its Droid Edition levels.

Only issue I had with it is that the battery drain is a wee-bit high. Though this may be due to the process of installing and optimizing apps over time. If it all goes well, the battery drain should calm itself soon. As of right now, I've downclocked the processor and changed the governor to be as efficient as possible to reduce that battery drain until the phone is fully-set up. The other issue is that after a while, CPU-Z and AIDA64 fails to find the big cores, saying that they're either inactive or "sleeping", but Kernel Adiutor said otherwise. Other than that, I am enjoying it.

Also goes to show that if you have the MM bootloader, you should definitely keep it as it provides a very safe method of returning to a previous build with all your system files intact if anything breaks. It has proved to be extremely useful in this case.