Only signed up here to say that I have the same issue.
Bought the mouse 3 or 4 days ago. Every time I leave it charging overnight on my Belkin Qi charger that I charge my iPhone XS with, the mouse becomes unusable in the morning. It is very hot to the touch, especially the bottom part. Even when I connect a wire to it, it won't become responsive. Had to wait for about 5 minutes for it to cool down, then it became usable.
I have a feeling that the Qi charger actually drains the battery. My iCue shows that I have 7% battery left after charging all night and I had about 40% left most likely when I put it on the charger at night.
I have submitted a ticket but Corsair has not responded yet. My advice to everybody is to stop using Qi chargers all together for the time being.
EDIT: Turns out that when you switch off the mouse before placing on charging matt it will not overheat!