Hello, I have met that situation before, I later figured out maybe there are some tips you should follow if you want to chang the location of your icons. When you drage icon 1 to change its location to where icon 2 locates, you need to make sure that icon 1 and icon 2 are excatly overlapped while draging, then icon 1 will locate where icon 2 initially locates.
If you try to drag icon 1 to the location between icon 2 and icon 3, sometimes it might be unsuccessful. Hope you will find this helpful.