I have had two iphone 6s and it has happened on both. I will set me lesson schedule in my phone (My google calendar is synced to my iphone calendar) and then set my alarms for both 5 minutes before each lesson and at the time of event of each lesson. Those work fine, but there is an additional, seemingly ghostly alert I receive always 24 hours before the lesson as well, which interrupts my lessons the day before. It's incredibly annoying, and I can't find the culprit anywhere. I've gone into my google calendar on my computer, and occasionally there is an added 1 day before alert. I then erase that thinking problem solved and it just keep happening. Help!