Make sure widget is set up to use custom widget zone: MainSlider
Section is a part of QuickProducts plugin, a part of Theme package.
Make sure you have set up widget zones for that sections. By default widget zones are set to "none".
That is because of design. If you have less than 6 items of bestsellers, missing places will be duplicate. If you will have more, duplicates will be replaced.
Section is build of topics. Need to look for topics system names banner_home_page_1 and banner_home_page_2