Chlorine dioxide is unstable. In a chlorous acid solution, the chlorine dioxide is constantly escaping the solution. If there is available chlorine dioxide in the mixture, then the chlorous acid breaks down a little in an effort to maintain the concentration of chlorine dioxide in the solution.
This is a gradual transition.
This allows you to mix up a batch of chlorous acid in the morning and wash vegetables with it all day and have it continue to be effective. In food processing a new batch is mixed up every morning because in use it only lasts a short term.
Storage is a little different. A mixed sanitizing solution of chlorous acid also will only be effective for a short time, but the time is weeks if the solution is properly stored. However, in the presence of UV light and in an open container the solution is only effective for minutes to hours.