It still boots into TWRP (luckily). I tried ADB sideload, and I manage to install ROMs with no issue, but the device boots right back into TWRP on its own. I also have access to download mode and tried the LG FlashTool but it doesn't do anything. I've followed the instructions for it and I just get the COM41 port saying "READY!!" and stays there.
Any advice would be greatly appreciated, he's been out of a phone for two weeks now.
Edit: This is the error on TWRP. "E:Unknown File System: 'datamedia'"
Edit: Fixed. I didn't set the phone to COM41 in device manager. Oops.