You can easily download the LG Flash Tool from the https://www.lgflash.com/. I've got the tool from there and it works perfectly. If you have any questions, you can ask from me.
My device got stuck on a boot loop. I was trying to unbrick it by using the LG flash tool which I got from the https://www.lgflash.com/. I am sure the tool has no any bugs or like that sort of thins. But I need to enter the firmware update mode fast. I already tried to turn my device on by...
I think the problem is there with your new firmware that you are trying to install. Make sure that you get the correct firmware and try it again. I usually gets my tools from the https://www.lgflash.com/. Their tools are great and easy to use. I think the problem is there with the firmware.