[G4 Q&A, Help & Troubleshooting] verluci:
Hi XDA,

This morning I was just browsing Reddit when my phone suddenly shut down. When I tried to restart it I found that it was stuck in a bootloop.

I can only seem to get into download mode. Hard reset just doesn't seem to be working. Maybe I'm doing it wrong, maybe it's broken, I'm not sure. I was running the low effort root, and hadn't modified anything recently. Using the 2014 flash tool just gives me a "Connection to server failed. Try again in a moment" error.

Does anyone have any idea how I can fix it?

Edit:

THE ONLY KNOWN FIX IS TO RMA AND THERE DOES NOT SEEM TO BE A WAY TO RECOVER YOUR DATA

For some more information, the issue appears to be purely hardware based, and based on this thread seems to have primarily occured in the last months. Our phones randomly died during regular usage, then most users reported that rebooting it showed the "optimizing apps" thing (I personally did not see this) and then it rebooted again and went into a bootloop. Reinstalling the software often succeeds but doesn't actually fix anything, as your phone will just start looping again (still worth a try though, maybe you have some other unfortunate issue?). I myself and multiple users have tried the following things (text stolen from [MENTION=1082288]dentralp[/MENTION] because he wrote it up in such a good way):

Attempted Fixes:

1) Tried using LG bridge

-it says its updating to marshmallow (succeeds)

-then sits at LG boot screen without looping

2) Flashtool 2014 - Europe OPEN H81510D.kdz

-said that it couldn't connect to server

-clicked ok

-clicked retry

-says S/W update in progress

-stopped due to an error

-This is on my main PC, had issues with Flashtool before, will check on my laptop and feed back

-Fails on 9%

3) LGUP

-Only see's my device when I enter download mode

-Says my device is unknown so won't do anything with it

-Restarted Computer

-Wants a .tot not .kdz, contrary to the guide posted - out my depth, whats the difference between a kdz and a tot?

-Click on upgrade

-Chose Europe OPEN H81510D.kdz

-Close and reopen LGUP

-Making sure Refurbish is chosen (kdz should still be active file)

-Click Start

-80% Reboots, Reboots, reboots, reboots...

-100% "Click here to continue" on computer

-Reboot

-Bootloop

4) Longshot

-now I assume that I'm back on lp, moving back to step 2 Flashtool 2014

-Connection to server failed

-ignored

-seconds later it starts flashing

-Bootloop

5) LGUP

-Same as 3 above, but with MM H81520a_00.kdz

-Complete

-Bootloop

-repeated to go back to Europe OPEN H81510D.kdz

edit 26-1-2016

LG finally recognized the issue. They state that the problem is a loose connector. Article here: http://www.androidauthority.com/lg-admits-g4-bootloop-problem-hardware-fault-669603/

As far as I can tell, the issue is not restricted to certain phones, but primarily phones with serial 505xxxxxxxxxxx appear to be victim to this.

UPDATE: PEOPLE ARE CLAIMING THERE IS A WAY TO SAVE YOUR DATA

People are claiming that you can save your phone and recover your data by disabling the Big core. This means disabling everything that makes your phone fast. It may be a good way to recover your data if it's critical, but I would not recommend it as a real permanent fix, since it does make your phone a lot slower (a phone has 4 little cores and 4 big cores, the little ones are very energy efficient but slow, and the big cores are fast but not efficient). I don't have a clue whether this voids your warranty or not, and I've not seen many people confirm that it's working either, but it's worth a try! More information on the comment by gabriel713281 here and in the reddit thread here.