Random letters being pressed with one key

I have several Dell 5190 2-in-1 Chromebooks that are showing the same symptoms. They come in with the complaint that some letters are inserting random characters while others are either shutting the Chromebook down or restarting it, or acting as the return key.

I made sure they are all set to the US Keyboard, I tried a powerwash, I even went as far as replacing the keyboard. Still, this continues to happen.

Any help would be greatly appreciated. I do not see any signs of water or liquid damage on these units. I also do not see anything wrong with the mainboard itself. It is just very random.