I shaved all the ribs off the bottom of the pad and the charger works near perfect now, about like 99% of the time. The plastic cover is definitely the problem.
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I have zero doubt that the problem was corrected with shaving the ribs. I just meant that the source of the problem could be two or three different issues and/or a combination of them.
I can get the same results of the wireless charger working consistently by putting a small amount of pressure on the phone when it's on the pad. I'm not really 100% sure if raising the actual charger slightly won't make a difference. Unlike the same units in other GM vehicles where the chargers are locked in place by screws, the one in the twins actually just sits on locator pins. I noticed my charger sitting below the plastic trim around it. This would physically locate the charger a couple of millimeters lower than the pad is designed for. Spacing up the charger to be flush with the surround (in my case) would provide the same result as shaving the ribs of the pad.
Additionally, in previous TSBs for other vehicles from GM, one solution was a software change to alter the output of the charger for compatibility with newer devices at the time. It would not surprise me to see a different pad design, a spacer or locator pin change and/or a software update.