I just fixed my nexus 5x bootloop issue. It is a hardware issue so don't waste time in downgrading or changing the stock ROMs. I learned it the hard way and lost all the data in the process. Here are the simple steps to resolve the issue:
1) Open the back cover using the plastic screw driver. I used old credit card. Start from the USB port and go upwards.
2) Remove all the screws from the inner black cover.
3) Carefully remove the battery connector, USB connector and 2 camera connectors.
4) Remove the battery using a flat tool. It might be a glued but will come out.
5) Lift the circuit board and remove the heat sheet using the plastic tool.
6) Notice the 2 black squares chipsets. We need to apply heat to the bigger chipset.
7) Take a hair dryer and use a aluminium foil to narrow down its opening. I made a cone with small opening and used tape to stick it to the hair dryer.
8) Use heat on the chipset for a minute or 2 till it gets a little hot. Press it with your hand and thumb. Do not overheat the chipset.
9) That is it. Put it back and test your phone. It worked for me.
Please tell me wich square, the red one? That's te ram memory, but below that ram module is located the infamous snapdragon 808, so f**k you lg. Same history as lg g4 and lg v10. A very bad welding that with the temperature changes finally breaks (9-14 months). People used to bake the motherboard at 275 degrees for 7 minutes or with a heat gun but after hours it will break again (the welding).
So, no more Lg for me. I can not even sell this cell phone that would be scam.