Are you allowing the connection on your phone? When you connect your phone to the PC for the first time and ADB is active, the screen must be on and unlocked as there's a prompt which you need to accept to allow that specific PC to talk to your device via ADB.
In saying that, I did have issues getting ADB/fastboot drivers for the G4 (the mini adb package we have on this site didn't work, nor did the drivers from LG), I think I ended up using this in the end -
https://forum.xda-developers.com/showthread.php?t=2588979