Make sure the the filters and slicers are inside of the group/tab that you want them to influence. You can over over the group or tab to see the outline of the item. When you are dragging the filter/slicer within the tab make sure the the blue dotted outline is within the yellow outline. If you are moving the filter/slicer too far over the edge the blue line will snap to the inside of the group/tab before the item gets placed outside of the group/tab.
I like to make sure that I have a ton of space to work with so I usually make my groups or tabs as big as I can without having to scroll.
Let me know if this helps. If not, could you provide a screenshot that includes where the slicer is?