I've had similar issues with my Pro1 since day 1, though I cannot restrict the phenomenon to a certain subset of keys. In the beginning, me trying to type fast always resulted in many errors, either from missing characters or from the software registering additional (e.g. "addd&nitional") keys, I certainly had not pressed.
Over time, I improved in hitting the keys "right", i.e., quite firmly and in a well-defined sequence. However, I cannot say that this kind of typing is much fun. I type slowly, and cannot practically use more than two fingers, even when putting the Pro1 down on a t