Every time data is extracted (and transformed) again, we compare it to the previously extracted data.
If no data transformation is specified, the entire extracted data is checked for changes - if a single attribute changes, the monitor will trigger a webhook again.
When you specify a transformation, only the transformed data is used to check for changes.
We're working on that. Please let us know your interest here.
If you're confident that wasn't just you who pressed "Test webhook", then that's a bug. Please report that monitor to us.