When you map two or more points that have the same latitude and longitude or geocode to the same address, only one of the points will show.
You can work around this limitation by altering your coordinates slightly or providing a location that geocodes to a slightly different address.
Geocoding only one column of a multi-column address, such as city, may also cause this situation. You can fix this by combining the columns into a single location column.
If you find the ability to map multiple points at the same location valuable, please add your star vote and describe your need in the feature request. The request thread contains some additional workarounds you might consider.