Let me begin by saying I am a Google Domain Admin for 10k users. I know my Googles.
However, even after following the instructions on this site, I have no clue how to prevent my calendar events from displaying twice. Take a look: http://www.slcusdcsea.org/events You look at the original calendar entry ICS file, https://goo.gl/oSaBpD , and it doesn't show duplicates. I'm not sure what I can do, I have tried removing the entire calendar, published, recreated using new calendar, it happens again... >Frustrating<