The Nexus 5X and Nexus 6P have been plagued with issues. If you’ve owned one of the devices or know someone who has, I’m sure you know about a few of the issues these phones have faced. One big issue is bootlooping, which is not uncommon and has not been fixed yet.
If you’re not satisfied with exchanging device after device or if you’ve run out of warranty, there may be a way to render your Nexus functional. However, it comes at a cost. The fix disables the “big” cores on the phone, leaving only half the cores, and the low power ones at that. The Snapdragon processors utilize the “big.LITTLE” architecture that switches between two sets of cores depending on how much processing power is necessary, and the big cores might be the issue here.
You’ll need to flash a custom version of TWRP and a modified boot.img file, which should neuter the device but make it functional. It’s unfortunate that you’ll be losing a majority of the device’s processing power, but at least your phone will work reliably.
Flashing your device with custom software is always risky and you need to know what you’re doing. You also need to understand the consequences of the mod, which will reduce performance in exchange for hopefully fixing the phone. If you’re interested, hit the source links for more info and instructions. And feel free to rant away in the comments about Google’s failures with these devices.