We really don't have enough context here to provide you any sort of insight. Where is that expression going exactly? Is it part of a query you're running to get the data to display? Is it tied to an expression you're using to show/hide a row, what?
We also don't know what any of the values in your expression represent. Is Box_Number
a parameter specified when running the report, a column in a table? It looks like a parameter to me based upon the rest of the query. If it is a parameter then how is it defined? Is it a multi-value parameter, single-value string, etc?
Just trying to interpret your query, it appears that if no box number is selected then it returns all rows that have a box number. Otherwise it attempts to filter out all rows that don't match that box number. But in that case the primary indicator on the county must also be set. In the row you said isn't showing up it doesn't appear to have a county so I wonder if the second part of your condition is causing it to disappear.