If an ExpenseConnect batch is not 100% successful (e.g. some reports failed for validation reasons), ExpenseConnect will keep trying to pull in the failed reports over and over again.
If you need to skip over those reports, you can check them as Integrated in the batch record. After you do that and run a fully successful batch, ExpenseConnect will use the date of that batch as the start date for future batches. So it won't go back in time to try to pulling old reports.