stackable items get stacked with non-stackable items in water flow and doesn't get sucked by hopper

I tried to create a water loop for  my zombified piglins gold farm, and the stackable items get stacked with non-stackable items in water flow, and never get sucked by hopper what so ever

I have video proof regarding it

[^Untitled.mp4] stacking items issue-1.mp4

[^Untitled.mp4] stacking items issue-1.mp4 stacking items issue-2.mp4