There is a small amount of flex in the keyboard of the one in my work, my A15 has a bit of flex also, most gaming laptops i have tried all have a bit of flex unless they have a metal frame.
The 2.5" drive bay is located near the enter key so if it is empty maybe that could be why there is flex although ours had a fake plastic hd in the bay before i fitted a drive in it.
The flex is of i press to the right of the # key not the key itself vut the board below the keys try the one at work see if a little flex but overall very impressed thanks so much for the help