To assist you further, would you please help me with the link to the portal that you are trying to submit your application?
A common reason that would lead to the application status change to Incomplete Application/Missing Info would be if your browser session had expired resulting in the form not saving information properly. Another reason would be if someone from the HR team changed the application status manually.
The Application status can be changed by the HR team and they can provide information on why the status was changed to Incomplete Application/Missing Info. I recommend working with the district's HR team who can help you with the status of the application.