Chances are you assigned it a non-existent order-status value.

Compare that order's order_status value against the available statuses in your orders_status table. You'll find that if it's not matching a value in the orders_status table then it won't properly show in your admin.

Simple fix: Use the admin order screen to search for that order number. Then update its status using the normal status-update options, choosing a valid status from the pulldown menu. That will set it to a valid value.

Or, edit the order_status value directly in the orders table in the database.