Ideally, if you have an unfilled order, 'repairing' the same would place a fresh order to complete your smallcase. If you are unable to repair the unfilled order, it could be due to the following reasons:
Stocks sold on Kite - If any of the stocks bought on smallcase are sold through Kite, the same wouldn't be updated in your smallcase due to privacy reasons. So, your smallcase would continue to show a stock that is no longer present in your holdings.
Short delivery - If any of the shares bought through smallcase are short delivered, the same doesn't get updated on smallcase. In this case, you would be notified by Zerodha regarding the short delivery of shares. More on short delivery
NRI account holders - Due to some restrictions specific to those with NRI accounts, there may be unfilled orders while rebalancing. Read more here.
For assistance in getting any of the above resolved, you may write to firstname.lastname@example.org.