Is your key diamond shaped?
Mine is not and I've had similar issues. The car will lock just fine but will maybe unlock 95% of the time. I ordered a new key and that didn't really change anything. The central locking button in the car acts the same way meaning it's the main locking system which ties into the GM. I can hear the mechanism clicking as I press the button but it just fails to unlock the doors.
Actually last week the key stopped unlocking AND locking the doors so I replaced the battery and it's back to normal. However the module I think still needs to be replaced or repaired.