Workaround: LG X Power locks up on firmware update
I have a possible fix for anyone who gets locked up on the firmware update screen and is not able to power down and/or boot up.
(The method I used can damage any phone. I do not make any warranties about the completeness, reliability and accuracy of this information. It worked for me and may not work for you. Any action you take upon the information contained in this post is strictly at your own risk and I will not be liable for any losses and damages in connection with the use of this information.)
LG tech support told me i needed to send in my phone to get repaired for 3 weeks. Unfortunately I had some time sensitive data on my phone that I needed to retrieve so this was not an immediate option. I was not able to retrieve said data in time and lost a bid on a contract due to this. In hope that I can save someone the headache, aggravation and loss of money that i went through here is what i figured out. After spending 5 hours researching I was finally able to boot back up. (This may only be a temp fix so I advise to follow LG's advice in sending the phone in to be repaired if they so request. This will at the least allow you to access your phone until such time).
If your phone is locked up on the firmware update screen w/ download percentage hanging at 0. I advise you to wait at least an hour before attempting this and make sure you are outside where reception is good in the off chance that the phone is trying to download but has poor reception. If at anytime the download progress bar rises above 0 percentage do not attempt this and contact a boost care representative.
If the phone is actually downloading the update and u attempt this you could damage the phone. This worked for me and at the time i was prepared to take the risk because of the time constraints.
1. On lockup screen hold the power button and the volume down button simultaneously. This will hard shutdown the phone.
2. After shutdown press the power button to reboot.
3. If the phone boots up you are good to go and can skip the next step.
4. If the phone boots up to the firmware update screen again wait another hour to see if it attempts to download. If the progress bar is still at 0 proceed to step 5.
5. Repeat steps 1 - 2. As the phone is rebooting hold only the power button pressed until you see that the phone has bypassed the firmware update screen.
Hope this helps.