On the LG G4 you can disable the BIG cores (cpu 4 and 5) and your phone will boot (even ultra bootlooped). I try this on a friend's phone (5x with infinite bootloop) and this worked, but now the big cores works too, so we dont know if this "possible fix" did something or its just a placebo effect and the bootloop issue on this device is due to something different.
I modified the ElementalX 1.20 Kernel (by flar2) just a little and now your phone will boot only with his A53 4 cores running (littles). so basicly it disables the big cores (2 A57) and lets the phone BOOT "aparently it works" (in that case that's where bad welding is).
Flash oficial factory image 6.0.1 MTC20K (or any marshmallow stock build compatible with elementalx 1.20).
Download: Elemental by flar 2 modified for ILAPO.zip (12.76 MB).
Download and flash the zip file and go trough the installation process normally (via Aroma
it does not matter if you configure the second cluster freq, anyway the big cores will be disabled).
Method 2: (Recommended)
Download: bootelx1.20.zip (12.05 MB).
Extract the .IMG file. and put it inside your ADB's program root folder.
Enter to FASTBOOT mode.
Open Minimal ABD and Fastboot (or the ADB/fastboot client that you want).
With your pone into BL (and connected via USB to the pc) run:
fastboot flash boot bootelx1.20.img
It only works for unlocked BL.
Please, try this and leave your comment.