We are aware that there are some errors that the system currently does not display.
This is usually because the particular error has not been seen by the system before, for example because it is not a common learner error. It could also be that the system has detected the error but is not confident enough to suggest what the problem might be. The system always tries to be very precise with the errors that it suggests, rather than offer suggestions that could be incorrect. It is also designed not to show too many errors, because this would be a bad experience for the learner and may cause them to lose motivation.
The good news is that, as more people use Write & Improve, the better the system gets at finding errors.