LG G3 Restart and Shut down automatically I have LG G3 (D855) and running stock firmware, Someday back my phone start showing invalid sim then i tried same sim with different phone and its working. Now i know there is some fault in phone, i was keep trying then after few minutes my phone restart with awkward loud beat and then shut down/restart to boot. To boot i need to take out battery but it still restart or shut down automatically.

I flashed my phone to stock KDZ successfully but still i am facing same issue. My screen sometimes stuck to LG logo or LG logo disappears and shut down (Need to take out battery to start my phone again), Boot sometimes to home screen then turn off. I flashed to D85530e_00_0927.kdz , which is stock i was using before any issue in my phone.

Please help me to fix my phone
Lots of LG phones are showing up bootloop issues. The issue you are facing can be closely related to other bootloop issues seen in LG phones. And if it is, I dont think you can do much to fix this issue. 

You may however give a try installing a light weight OS like lineage OS. I had faced similar situation with Nexus 5x. Installing Lineage OS helped a bit(restarts/sudden shutdowns became less frequent). In my case replacing motherboard solved the issue for me.