They might even claim the 3rd party charger is too strong for LG battery and damaged the phone.
That would be rubbish because the charger is rated at 5 volts, the exact same voltage as LG, as every phone charger. If my valore charger was in excess of 5V, then thats where the danger comes in but then the valore charger would be a danger to every consumer electronics that is rated 5 volts USB charging.
The current (amperage) needs to match or exceed the amount required by the phone. If it exceeds, then thats where the 'fast' charging extra supply comes from. Since amperage is tied to the power draw of the device, the more you give, the faster it will charge, unless it is consuming high power under load (eg. intensive gaming).
The final point of my argument to the CSO is that I used the same chargers (I have more than one, at different venues) on the phone and never experienced this issue until after the LCD replacement (which was last Wed) and I experienced the issue on all fast chargers I own.
Since i passed them my phone + my charger I hope the technician is at least savvy enough to conduct a proper A/B testing on my G4 vs their own G4.
Try other QC2.0 chargers u can get hold of, especially the original first-party ones as they tend to use better internal components.
I have a hunch that your Valore chargers are not giving out clean voltages, or have a noisy ground that wrecks havoc with the G4 touchscreen.
During the month of january when i got back my bootloop-fixed G4, they flashed MM onto the replacement motherboard and i already had to spend money on a replacement battery just to be sure it was MM having messed up battery life and not my own battery dying.
At the moment I'm not about to entertain the thought of assembling a collection of QC chargers, would be too expensive as a troubleshooting effort