[G4 Q&A, Help & Troubleshooting] S4mpe:
LG G4 815

S/N=511

tl;dr: Bootloop, did a lot of fiddling, finally ended up with installing a "somewhat" working setup in this order (Everything installed via TWRP, TWRP was via fastboot):

1. TWRP (SteadfasterX's) /O version

2. V29a Firmware, keep TWRP

3. Disable big cores kernel (From above V29a firmware thread, first reply by kessaras)

4. LineageOS 15.1

5. Mindthegapps

Having troubles getting it to boot past the LG bootscreen (Once it boots completely, it seems to work fine).

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So yesterday I was browsing my phone when it suddenly restarted. It had done this before multiple times and it always has gotten back to working just fine. Only this time was different, after the LG bootscreen went away, it appeared again. I'm aware of the bootloop issues the device has and was hoping I would get lucky but apparently not.

Configuration when bootloop happened:

-LineageOS14.1

-Stock kernel

-TWRP (3.1.1?, cant remember exact version it was 3+ anyway).

I noticed I could still access TWRP (Although it did crash few times back to LG bootscreen), so I first tried wiping caches etc (No luck). Anyway, I was quite close to just giving up at this point, but decided to fiddle around with the thing. I found out about the issue with one of the "big cores" heating too much and that it was possible to disable those. I decided to give it a try, and while I was at it, wanted to try out the newer LOS15.1. Downloaded titan kernel (no big cores), installed and went onto install LOS. First issue, my TWRP wasn't new enough to install the LOS15.1 (Error code 7). Did some searching and found out about "unofficial TWRP" installations that allowed me to install LOS15.1 (Used SteadfasterX's TWRP, O/ version).

After this I got a few kernel crashes (Green screen with a lot of text, different error codes each time), all searches pointed to my own error during installing stuff (I had older firmware while LOS required newer), and I believe these crashes had nothing to do with the actual bootloop issue. To fix this I went and grabbed the V29a firmware and the big cores disabled kernel which is in the first reply of that v29a thread. After this I managed to install LOS15.1+Mindthegapps (Also rooted it) just fine and it booted up past the LG bootscreen. I grabbed Kernel Auditor to check if the big cores had been disabled and I could only see 4 cores (max 1,44ghz).

Now the phone seems to run fine when I actually get it booted up. I tried restarting the phone and I was stuck in the loop again (Did multiple restarts). I tried booting into recovery (I got into the "factory reset" dialogs just fine which takes you to TWRP) but after that instead of TWRP it went back to the LG bootscreen (Tried again like 3 times). After this I plugged in my phone to my computer and got into TWRP first try(I wonder if there's an actual reason for this, I know it could be just pure luck). Then I went onto the reboot options in TWRP and booted into system. First time I got past the bootscreen but it crashed when asking for my SIM pin code. Second time after booting the same way, I got it working just fine and now the phone seems to be working happily again.

Is there anything I can do myself to trace this issue and improve the chances of booting up the phone or am I forced to just rely on luck and hope it boots completely without crashes (In the case of a crash/I need to restart the phone)?