Frequently, this is due to the map icons being “stacked up” at the exact same location.

You can zoom in on the map to see if there is another one “underneath" the icon. Or look at the lat/lon of each structure.

Before (two preplans at the exact same address were atop of one another):

You can refer to this help guide for how to manually nudge a structure's coordinates.

After I manually move the location of the preplan address: