I'm so CONFUSE with the UNIQUE COUNT

on my work i used the Unique count metric and suppose the value is 6 << remember this value

and then i would make a metric visualization i used unique count and i play value is 6 still ok but then I Filters this

on my Discover Page and value is 0

then i copy this filters above and pates into Filters Bucket and value STILL 6 !
i have a question why the value still 6. I Filters in Discover page and value is 0 but i Filters on Bucket value is 6 << (6 is value of UNIQUE COUNT)

Which version of Kibana are you using? It might be that you're using KQL here inside Discover, but using Lucene inside your filters bucket in the visualization.