In rare cases, a polling trigger cannot recognize that an item is not new, so it triggers the Zap from previously seen information. This can happen when:
A large number of items are deleted from the trigger app, causing older items to be surfaced and picked up by the Zap.
You delete items, thereby changing the position of older items (the row where that information is in, for example). This causes the Zap not to recognize that item, as it may use a combination of content and position to recognize duplicates.
If you need to make significant changes to items in your app that's linked to a Zap, you can turn the Zap off until all changes are completed, and then turn it back on.