Following a recent Office 365 upgrade, I did not change the individual occurrence in any way from its series... However, I did notice the day/time of the series in question coincides with another series on my calendar during the same day/time. Both series have the recurrence symbol with a line going thru it...
It means "Exception to recurring item".
http://www.howto-outlook.com/howto/icons.htm
Following a recent Office 365 upgrade, I did not change the individual occurrence in any way from its series... However, I did notice the day/time of the series in question coincides with another series on my calendar during the same day/time. Both series have the recurrence symbol with a line going thru it...