Hi Ronivil,
Thank you for sharing the action flow, I think I see your issue.
1) Please make sure when you are retrieving data from a server call that the data is fetched and the list is not empty!
2) Assign the whole output to a local variable, in which you will perform the listfilter.
3) In the listfilter assignment, you check the current Profile.LastName but not the whole set, rendering the filter pretty much useless. Either iterate over all results or use the whole list as a filter.
4) As Khuong mentioned, it is a good practice to clear previous results before appending to prevent contamination of results.
Hope this helps!
Gr