Hi Samwise
The FDX filter filters the original FDX result. So that means it will only apply if the filter conditions are met e.g those values exist in the dataset returned from your original data unit FDX call.
If the filter criteria is not met. The filter does not apply.
So I suspect there is something awry with your filter. Maybe run the original data set without filters. Check if these values you are filtering by exist and then slowly build your filter (where clause) e.g start with Flow on its own
The behaviour you are describing sounds like one of your filter conditions is not met. Since your filter is using AND it implies that all of your filters need to be valid in order to invoke the filter
Hope this helps
Sam